1

COLOUR PHYSICALISM, NAÏVE REALISM, AND THE ARGUMENT FROM STRUCTURE

Keith Allen, University of York

keith.allen@york.ac.uk

Forthcoming in a special issue of Minds and Machines edited by Mazviita Chirimuuta.

Please refer to the published version.

Abstract: Colours appear to instantiate a number of structural properties: for instance,

they stand in distinctive relations of similarity and difference, and admit of a fundamental

distinction into unique and binary. Accounting for these structural properties is often

taken to present a serious problem for physicalist theories of colour. This paper argues

that a prominent attempt by Byrne and Hilbert (e.g. 2003) to account for the structural

properties of the colours, consistent with the claim that colours are types of surface

spectral reflectance, is unsuccessful. Instead, it is suggested that a better account of the

structural properties of the colours is provided by a form of non-reductive physicalism

about colour: a naïve realist theory of colour, according to which colours are superficial

mind-independent properties.

1. The Argument from Structure

Colours appear to instantiate a number of characteristic ‘structural’, or ‘higher-order’,

properties. First, they stand in distinctive relations of similarity, difference, and

exclusion: for instance, orange is more similar to red than orange is to blue, no shade

of yellow is a shade of red, and so on. Second, the colours admit of a fundamental

distinction into unique and binary (or compound more generally). Unique colours are

‘pure’ or ‘perceptually unmixed’ instances of the hues yellow, red, green, and blue and

the achromatic colours black and white. Binary colours, by contrast, are always a

‘perceptual mixture’ of two other unique colours: for instance, orange is a perceptual

mixture of red and yellow, cyan is a perceptual mixture of blue and green, grey is a

perceptual mixture of black and white, and so on. (Compound colours more generally

are perceptual mixtures of more than two unique colours: for instance, brown is

perceptual mixture of red, yellow, and black.)

The structural properties of the colours are often taken to have a special status.

The structural properties are not merely contingent properties: properties that the

colours could have failed to instantiate. Rather they are necessary properties—

properties that the colours instantiate in all possible worlds in which they exist—or

perhaps even essential properties—properties which serve (at least in part) to

individuate the colours, and in virtue of which the colours are the things that they are,

and not anything else.1 On this view, orange (for instance) is necessarily more similar

1 The claim that the structural properties are necessary properties of the colours is not always sharply

distinguished from the claim that they are essential properties. But necessary and essential properties

are not obvious identical: as Fine (1994) argues, Socrates is plausibly necessarily, but not essentially, a

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to red than blue and a perceptual mixture of red and yellow, and indeed part of what

it is for a colour to be orange is for it to be more similar to red than blue and a

perceptual mixture of red and yellow: orange simply would not be the property it is if

did not instantiate just these structural properties. The view that the structural

properties of the colours are essential properties of the colours is described as a core

common sense belief about the colours by Johnston, according to whom:

Thanks to its nature and the nature of the other determinate shades, canary yellow, like

the other shades, has its own unique place in the network of similarity, difference and

exclusion relations exhibited by the whole family of shades (1992: 138).

Similarly, defending the claim that the colours instantiate the structural properties

necessarily, Hardin argues that:

If we reflect upon what it is to be red, we readily see that it is possible for there to be a red

that is unique, i.e. neither yellowish nor bluish. It is equally apparent that it is impossible

for there to be a unique orange, one that is neither reddish nor yellowish. Since there are

necessary properties of hues, nothing can be a hue without having the appropriate

properties necessarily (1993: 66).

If the structural properties of the colours are necessary or essential properties of the

colours, this in turn sets constraints on what the colours could be: the colours will be

those properties that instantiate the relevant structural properties.2

The structural properties of the colours have been widely discussed in the

philosophical literature. It is misleading to talk of ‘the Argument from Structure’, since

the structural properties of the colours have featured in a number of related

philosophical arguments, each with slightly different premisses and conclusions.3

However, a common target of arguments that appeal to the structural properties of

the colours are views according to which colours are physical, min-independent, member of the singleton set {Socrates}. The essentialist claim seems to me to better capture the content

of the relevant intuition, although I will not argue for this here. Note that the weaker claim that the

structural properties are necessary properties of the colours is sufficient to set non-trivial constraints on

what the colours could be. 2 The claim that the structural properties of the colours are essential properties of the colours is

consistent with treating colours as kinds, assuming that kinds have certain properties essentially.

However, it is does not necessarily imply that colours are natural kinds, if this means that colours are

properties with a complex physical or micro-physical essence. According to the naïve realist theory of

colour defended below, colours are better thought of as superficial kinds. See also Author. 3 Some versions of the Argument from Structure do not rely on the claim that colours are necessary or

essential properties of the colours. The version of the argument presented here is more controversial in

this respect, but stronger as a result. The distinction between non-modal and modal versions of the

argument is noted by Cohen (2003); see §2 for some discussion.

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properties of things in the environment. Specifically, these arguments are typically

directed against reductive physicalist theories of colour, according to which colours are

(‘narrowly’) physical properties: for instance, types of surface spectral reflectance (e.g.

Byrne and Hilbert 1997, 2003, Tye 2000), or else microphysical properties of objects

(e.g. Jackson 1996). According to one way of developing this line of argument:

The Argument from Structure

1. The structural properties of the colours are essential properties of the colours; 2. There are no physical properties of things in the environment that instantiate

the structural properties of the colours; 3. If colours are physical properties of things in the environment, then everything

that is true essentially of the colours is true essentially of these physical properties;

4. Therefore, colours are not physical properties of things in the environment.

This general style of argument is employed by Berkeley’s spokesman Philonous in

response to Hylas’s physicalistic identification of sounds with motion:

PHILONOUS. …are you sure then that sound is really nothing but motion?

HYLAS. I am.

PHILONOUS. Whatever therefore agrees to real sound, may with truth be attributed to

motion.

HYLAS. It may.

PHILONOUS. It is then good sense to speak of motion, as of a thing that is loud, sweet,

acute, or grave. (Berkeley 1713/1734: 172).

More recently, this form of argument has been presented in response to reductive

physicalist theories of colour by Hardin (1993), Maund (1995), Thompson (1995),

Pautz (2006), and Dorsch (2010) amongst others.4

After briefly considering premisses (1) and (3) of the Argument from Structure

in §2, §3 considers in detail a prominent physicalist attempt to reject premiss (2). I will

argue that this response is ultimately unsuccessful, and in §4 present a different way of

rejecting premiss (2) that appeals instead to a form of non-reductive physicalism about

colour: a naïve realist (or primitivist) theory of colour according to which colours are

superficial mind-independent properties.

4 Related argument with epistemic premisses are presented by Boghossian and Velleman (1991) and

Johnston (1992). Johnston, for instance, argues that if colours are physical properties, then their

structural properties could only be discovered by empirical investigation. But this violates a what he

takes to be core common sense belief about the colours, Availability, that ‘Justified belief about the

canary yellowness of external things is available simply on the basis of visual perception’ (1992: 138).

The advantage of the present argument is that it does not appeal to this principle, which it would be

open to physicalists to reject.

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2. Premisses (1) and (3)

One response to the Argument from Structure is to reject premiss (1). A popular way

of denying premiss (1) consistent with a physicalist theory of colour is to deny that

colours instantiate the structural properties essentially, by distinguishing between

colours and colour experiences and reinterpreting premiss (1) as a claim about our

colour experiences. On this view, the colours themselves may still instantiate various

structural properties in virtue of structural properties of the experiences that these

properties produce; however these properties are essential properties only of colour

experiences, and not of the colours themselves. A consequence of this is that the

properties identified with the colours could produce different experiences with

different structural properties, and so could themselves stand in different relations of

similarity and difference (e.g. Lewis 1997; Cohen 2003; McLaughlin 2003).5

One advantage of this approach is that it provides a way of recognising the

seemingly close relationship between the way colours appear and the way that the

visual processing mechanisms underlying colour experience function (although I

return to this in §4). At the same time, this view goes at least some way towards

respecting the appearances, at least to the extent that colours are, as they appear to

be, mind-independent properties of things in our environment.6

The main problem with this view is that it appears to get things the wrong way

around. On the face of it, colour experiences appear to stand in distinctive relations of

similarity and difference because of relations of similarity and difference between the

colours, and not vice versa. This follows naturally from the phenomenological claim

that perceptual experience appears to be transparent—that when we reflect upon our

experiences, we are only aware of objects, properties, and relations in the environment,

and not any properties of the experience itself—and hence that our experiences

appear to ‘inherit’ their qualitative or phenomenal character from that which they are

5 An alternative way of developing this general line of response is to argue that the structural properties

are properties of experience that are falsely attributed to the colours (e.g. Churchland 2007). This is

problematic for broadly the same reasons as the view considered in the text. A more radical response is

to deny that the structural properties of the colours are essential properties of anything at all, as

opposed to being artefacts of our linguistic representations (e.g. Saunders and van Brakel 1997; Mizrahi

2009). I will not address this form of relativism here, but for some relevant discussion see Jraissati

(2014). 6 The phenomenological claim that colours appear to be mind-independent properties of things in the

environment—rather than, say, mind-dependent dispositional or relational properties—is sometimes

denied (e.g. Cohen 2009; Chirimuuta 2011). However, for defences of this claim, see e.g. Author;

Roberts, Andow, and Schmidtke (forthcoming).

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experiences of.7 There is no obvious phenomenological difference in this respect

between colours and their structural properties: just as colours appear to be mind-

independent properties of things in our environment, the structural properties

associated with the colours appear to be mind-independent properties of properties of

things in our environment, not properties of our experiences themselves. Given the

transparency of experience, the claim that the structural properties are primarily and

essentially properties of colour experiences, and that colours only instantiate the structural

properties derivatively and contingently, is liable to seem to mislocate the locus of the

relevant essential truths. These considerations may not provide absolutely conclusive

reasons for rejecting this type of approach: for instance, proponents might be

prepared to accept these seemingly counterintuitive consequences (Lewis 1997), or try

to explain them away (Cohen 2003). Nevertheless, they provide a motivation for

considering alternative responses to the Argument from Structure.8

Premiss (3) of the Argument from Structure is an application of Leibniz’s Law.

Without denying Leibniz’s Law outright, an alternative response to the Argument

from Structure is to attempt to restrict its application in the present context—for

instance, by denying the claim that the structural properties of the colours should be

evident from the physical description of their nature. On this view, the structural

properties of the colours would be evident only on the basis of visual perception, even

though the colours would themselves be physical properties. The challenge for this

approach is to make sense of the fact that the structural properties are essential

properties of the colours, without conceding that they have a nature that is, at least in

part, not (narrowly) physical. On the one hand, if the structural properties of the

colours are evident only on the basis of visual experience because (for instance) visual

experience provides a contingent mode of presentation for the physical properties that

are identified with the colours, then this undermines the claim that the structural

properties are essential properties of the colours. On the other hand, if the structural

properties of the colours are essential properties of the colours that are not evident

from the physical perspective, then, as Byrne (2003: fn. 5) suggests, this begins to

sound more like a dual aspect theory than a full-blooded form of reductive

physicalism, since physicalists typically insist that a thing’s essential properties are

those that are captured by the physical description of their nature.9

7 On the ‘inheritance’ metaphor and its relationship to the transparency intuition, see e.g. Campbell

(1993); Shoemaker (2003); Kalderon (2011). 8 For more detailed discussion of problems with versions of this approach, see e.g. Byrne (2003); Pautz

(2006); Cohen (2009); Davies (2014). 9 Davies (2014) defends a view of this kind, comparing this response to ‘type-B’ physicalist accounts of

the mental. Davies’s defence of this approach is programmatic, noting that colour physicalists can

adapt whatever turns out to be the best type-B physicalist account of the mental. Assuming that a viable

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3. Premiss (2): Reflectance Physicalism

Given a presumptive motivation for accepting premisses (1) and (3), an alternative

response to the Argument from Structure is to reject premiss (2), the claim that there

are no physical properties of things in the environment that instantiate the structural

properties characteristic of the colours. This section considers one way of developing

this line of response; an alternative is suggested in §4.

3.1 Byrne and Hilbert’s Reflectance Physicalism

According to a popular form of colour physicalism, colours are identical with types of

surface spectral reflectance (SSR).10 SSRs determine the proportion of the incident

light that an object reflects at each visible spectral wavelength; colours are identified

with types of SSR to accommodate metamers, objects that differ in SSR but which

nevertheless appear identical in colour (at least in certain conditions). SSRs types are

individuated in terms of the relative proportions of the incident light that objects

reflect across different broadband regions of the visible (to humans) part of the

electromagnetic spectrum. Such properties are not very interesting from a physical

point of view, but are nevertheless mind-independent (Hilbert 1987). And although

surface spectral reflectances are relatively high-level physical properties—in contrast,

for instance, to their micro-physical realisers—this is still a form of reductive physicalism

to the extent that colours are identified with properties described by the physical

sciences.

On the face of it, SSRs do not appear to instantiate the characteristic

structural properties of the colours: for instance, if we consider sample SSRs for red,

orange, and blue, there need be nothing about these SSRs that would lead us to

expect that the first is more similar to the second than it is to the third; similarly, if we

compare the SSRs for unique red and orange there need be nothing that would

obviously justify the description of one as unique and the other as binary (Byrne and

type-B physicalism about the mental is forthcoming, it would still need to be shown that this approach

can be adapted to allow for experience to provide knowledge of essential structural properties of the

colours without collapsing into a form of a dual aspect theory. Type-B physicalists often appeal to

phenomenal concepts to explain the different mode of access to physical properties that experience

provides. However, phenomenal concepts are often taken to provide only a ‘thin’, demonstrative,

characterization of their referents, in which case it is difficult to see how they could provide substantive

knowledge of the essential structural properties of the colours. Alternatively, if phenomenal concepts

provide more substantive characterisations of their referents that allow for knowledge of their structural

properties not provided by physical concepts (as e.g. Schroer 2010 suggests), then it begins to sound as

though colours are properties whose essential nature is not fully physical. 10 Or to account for coloured light sources, types of productance more generally (e.g. Byrne and Hilbert

2003). However, I will focus on SSR’s here.

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Hilbert 2003: 13).11 Nevertheless, Byrne and Hilbert (1997, 2003; see also Tye 2000)

have argued that it is possible to account for the structural properties of the colours

consistent with the view that colours are types of SSR. I will focus here on Byrne and

Hilbert’s most recent proposal, which comes in two parts: first, a thesis about the

representational content of colour experience; and second, a thesis about the

properties that these experiences represent.

According to the first thesis, the representational content of colour experience

has an underlying complexity (see also Sundström 2013). Focusing in the first instance

on experiences of hues, colour experiences do not simply represent objects as having

determinate colours, but rather represent objects as having determinate colours in

virtue of having ‘proportions of hue-magnitudes’. Hue magnitudes are sets of

properties combined with ratio scales: functions that map these properties onto the

real numbers. There are four hue magnitudes: R, Y, G, B. Objects are represented as

having values of up to two of these hue magnitudes in different proportions: for

instance, an object instantiating a binary hue like orange might be represented as

having values of R and Y that are each 50% of its total hue; an object instantiating a

unique colour like unique green will be represented as having a value of a single hue

magnitude (in this case G) that is 100% of its total hue. Although Byrne and Hilbert

focus on hues, this account can be generalised by introducing achromatic magnitudes

Bl and W. Achromatic objects (white, gray, black) will be represented as having values

of one or both these magnitudes, whereas objects instantiating ‘tonal’ colours (e.g.

olive, pink, brown) will be represented as having values of up to two chromatic and

two achromatic magnitudes.

This thesis about the representational content of colour experience is then

combined with a thesis about the properties that these experiences represent. The

light that objects reflect can be characterised in terms of the degree to which it

stimulates the three types of cones (L, M, S) in the eye. The responses of these cones in

turn determine the way in which the retinal signal is processed in three opponently

organised psychophysical channels. To use a simplified model, L-M determines the

red-green signal (L-M > 0 red, L-M < 0 green), (L+M)-S determines the yellow-blue

signal ((L+M)-S > 0 yellow, (L+M)-S < 0 blue), and L+M determines the achromatic

signal (L+M > 0 white, L+M < 0, black).12 Using ‘L*’, ‘M*’ and ‘S*’ to refer to the

11 The microphysical properties of objects with which some physicalists identify colours appear even less

plausible candidates for instantiating the relevant structural properties. 12 It was initially thought that opponent cells in the laternal geniculate nucleus (LGN) discovered in the

1960’s were the neural realisers of the psychophysical opponent channels hypothesised by Hering to

explain (amongst other things) the unique-binary structure of the hues. However, it now seems that

experiences of the unique hues cannot be explained solely by the activity of opponent cells in the LGN

firing in response to signals from the retinal receptors, and a third stage of processing has been

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degree to which light of a certain kind stimulates the different cones in the eye, an

object has a value of the hue-magnitude R if and only if (iff) it has an SSR of the SSR-

type which would reflect light with a greater L-intensity than M-intensity (L*-M* > 0),

and the greater the difference, the higher the value of R. Similarly, an object has a

value of the hue-magnitude G iff it has an SSR of the SSR-type which would reflect

light with a greater M-intensity than L-intensity (L*-M* < 0), and the greater the

difference, the higher the value of G; an object has a value of the hue-magnitude Y iff

it has an SSR of the SSR-type which would reflect light whose L+M-intensity is

greater than its S-intensity ((L*+M*)-S* > 0), and the greater the difference, the

higher the value of Y; and an object has a value of the hue-magnitude B iff it has an

SSR of the SSR-type which would reflect light whose L-intensity is greater than its

M+L-intensity ((L*+M*)-S* < 0), and the greater the difference, the higher the value

of B.

This in turn grounds the following account of the structural properties of the

colours. Similarities between the colours are explained in terms of similarities in hue

magnitudes. For instance, orange is perceived to be more similar to red than it is to blue

because orange objects are perceived to have (say) a 50% value of the magnitude R

and red objects (if they are unique) are perceived to have a 100% value of the

magnitude R, whereas blue objects (if they are unique) are perceived to have a 0%

value of the magnitude R. Correspondingly, the property identified with orange is

more similar to the property identified with red than the property identified with blue

because the orange and red objects both reflect light whose L-intensity is greater than

its M-intensity (i.e. both have values of the magnitude R), whereas the blue object (if it

is unique blue) reflects light whose L-intensity is equal to its M-intensity.

Finally, the distinction between unique and binary colours can be explained by

reference to the proportions of hue magnitudes that objects are represented as having.

Objects instantiating binary hues are always perceptually represented as having non-zero

proportions of two hue magnitudes: for instance, orange objects appears both reddish

and yellowish because orange objects are represented as having non-zero proportions

of R and Y. Objects instantiating unique hues, in contrast, are always perceptually

represented as having 100% value of a single hue magnitude: for instance, objects that

are unique red appear neither bluish nor yellowish because they are represented as

having a proportion of the magnitude R that is 100% its total hue. Corresponding to

this, objects instantiating binary hues are such that they have non-zero values of two

hue magnitudes, whereas objects that instantiate unique hues have a non-zero value of

hypothesised, the neural basis for which has yet to be identified (e.g. De Valois & De Valois 1993;

Abramov 1997; for discussion, see e.g. Jameson and D’Andrade 1997; Jraissati 2014; Degenaar and

Myin 2014).

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just one hue magnitude. So, for instance, an orange object reflects light whose L-

intensity is greater than its M-intensity (L*-M* > 0) and whose L+M-intensity is

greater than its S-intensity ((L*+M*)-S* > 0), whereas an object that is unique red

reflects light whose L-intensity is greater than its M-intensity (L*-M* > 0) and whose

L+M-intensity is equal to its S-intensity ((L*+M*)-S* > 0).

If successful, Byrne and Hilbert’s account provides a way of denying premiss

(2) of the Argument from Structure consistent with the thought that colour

experiences inherit their qualitative character from that which they are experiences of.

The following subsections consider the two parts of Byrne and Hilbert’s proposal in

turn.

3.2 Do Experiences Represent Hue Magnitudes?

An obvious concern with the first part of Byrne and Hilbert’s proposal is that it

ascribes too great a complexity to the representational content of experience. After all,

experience is often taken to present colours as perfectly simple properties; as Locke,

for instance, puts it, ideas of colour are simple ideas ‘which being each in it self

uncompounded, contains in it nothing but one uniform Appearance’ (1690: II.ii.1).13 This

part of Byrne and Hilbert’s proposal therefore requires justification.

Byrne and Hilbert motivate the claim that experience represents objects as

coloured by representing them as instantiating different proportions of hue

magnitudes as follows. In the case of binary hues, they argue that 1) orange objects

(for example) appear to be a ‘mixture’ of red and yellow in the sense that they appear

to be both reddish and yellowish, and 2) they appear to be both reddish and yellowish

because they are perceived as having different proportions of the two hue magnitudes,

R and Y (similarly for the other binary hues). 1) is intended to rule out some

unsatisfactory ways of understanding ‘perceptual mixture’: for instance, that orange is

produced by physically mixing red and orange; that orange things appear to be both

red and yellow (that is, appear to have a conjunctive property—cf. Byrne 2003: fn. 38;

Byrne and Hilbert 2003: fn. 43); and that orange things appear to be composed of

smaller red and orange pieces, in the way that we might see both peas and beans in a

stew (to use an example from Hering 1920; cf Byrne and Hilbert 2003: fn. 43). 2) is

intended to give a specific account of the first part of the proposal. Byrne and Hilbert

motivate 2)—their explanation of the appearance of reddishness and yellowishness in

terms of hue magnitudes—as follows:

13 Even if you reject the Lockean simplicity intuition, it is further question whether colour experience

exhibits precisely the kind of complexity that Byrne and Hilbert ascribe to it. See Sundström (2013) for

discussion of two different ways colours might appear to be complex, only one of which corresponds the

complexity attributed by Byrne and Hilbert.

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It is natural to say, and subjects do say, that one colored chip has “more blue” and “less

red” in it than another, that a certain yellow chip has “no red and no orange” in it, that

any orange chip has “some red and some yellow” in it, and so forth. If subjects are asked

to estimate the “relative amounts of hues” in a stimulus (for example 40 percent red, 60

percent yellow), not only do they seem to understand the instruction, but they give

similar answers (2003: 14).

The judgments about relative hue proportions that Byrne and Hilbert refer to

are used in the Natural Colour System (NCS) to generate a colour ordering system

(see e.g. Hård et al 1996; Sivik 1997). The assumption appears to be that the ease and

consistency with which subjects are able to make colour appearance judgments of this

kind is best explained by the hypothesis that these judgments reflect the way that

colours are standardly represented in experience, and that subjects are able to make

these judgments by, in effect, ‘reading off’ the content of their experiences. In what

follows, I want to raise two concerns with this suggestion. First, the ease and

consistency with which subjects are able to make colour appearance judgments should

not be over-estimated. Second, Byrne and Hilbert’s is not the only available account

of these judgments.

On the first point, there are some important limitations to the ease and

consistency with which subjects are able to make judgments about the relative

proportions of colours that a stimulus contains. Intra-subjectively, consistency varies

both between subjects and between tasks: Shamey et al (2010), for instance, found that

intra-subject variability increases by around 50% if subjects are asked to make direct

judgments about the relative hue proportions that individually presented samples

contain, compared with a task in which subjects can compare and order a set of

physical samples presented simultaneously. Inter-subjective variation is greater than

intra-subjective variation. Inter-subjectively, judgments about relative hue proportions

are only roughly consistent (according to Sivik (2007: 180) within around 3-5% at a

.95 confidence-level), and there are differences, in particular, in the identification of

instances of the unique hues (Shamey et al 2010; Shamey et al 2011).14 The samples

used in the atlas that illustrates the NCS are the result of statistical analysis of the

cluster of responses that the hue estimation procedure produces (Sivik 1997: 179-180;

Matthen 2005: 89), and as a result the NCS atlas is unlikely to match all the

judgments of any particular perceiver. Consistency also varies across colour space.

Byrne and Hilbert focus on judgments about the relative proportions of hues in a

stimulus. But very few of the colours we normally perceive are fully chromatic, and in

14 For instance, Shamey et al (2011) found that the majority of subjects agreed with the physical sample

that the NCS describes as unique red, they mostly agreed with NCS unique green, but a majority

disagreed with the samples described by the NCS as unique blue and yellow. In each case, the mean

samples picked as representing unique hues varied between subjects.

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full generality their proposal will need to include judgments involving blackness and

whiteness: both for achromatic colours (black, white, and grey) and ‘tonal’ colours that

involve up to two hues and up to two achromatic colours (for instance, olive, brown,

pink). Focussing on judgments about relative hue proportions is liable to make colour

appearance judgments seem easier and more consistent than they generally are:

Shamey et al (2011), for instance, found that subjects find it significantly more difficult

to reliably judge the composition of achromatic colours (up to half erroneously

including chromatic components) and ‘tonal’ colours that involve up to four

components.

Besides, achieving these levels of consistency requires training participants for

up to fifteen minutes, and relies on using a ‘forced choice’ paradigm in which subjects

are prompted to describe colour samples only in terms of differing proportions of

unique instances of the six elementary colours identified by Hering: red, blue, green,

yellow, black, and white. The forced choice paradigm, however, dramatically reduces

variation. If no restrictions are placed on the list of basic colours which can be used to

describe samples, then the number of basic colours used increases. For instance, many

subjects find it difficult to describe brown samples using any other term than ‘brown’;

even Hering (1920) thought that identifying brown as orange (i.e. yellow and red) and

black was by no means obvious. Other potentially problematic colours include

orange, purple, and pink (Fuld et al 1982). It has been shown that subjects can

typically describe browns, oranges, purples, and pinks in terms of Hering’s elementary

colours if prompted. But the fact that prompting is required raises a doubt about

whether coloured objects are always represented in experience as having differing

proportions of the magnitudes B, Y, R, G; indeed, it might seem to lend some

support to the claim that they can be represented as having proportions of further

magnitudes, such as Br (brownish), O (orangish), Pi (pinkish), Pu (purplish). Green

raises the converse problem, because a number of people are inclined to describe

green in terms of blue and yellow.

Indeed, it is worth noting that even after training, some subjects are liable to

make ‘errors’ (from the perspective of the NCS) in describing colour appearance.

Shamey et al (2010), for instance, found that only 18 out of 30 subjects reliably

described hues in ways permitted by the NCS; the remaining subjects described some

colours in terms of opposing unique hues (for instance, green in terms of blue and

yellow), sometimes used three unique hues to describe a particular sample, or in two

cases simply had ‘conceptual problems with the task’. Moreover, whether all these

judgments are in fact ‘errors’ is itself controversial. Although now widely accepted,

there is a history of theoretical resistance to Hering’s identification of four elementary

hues, instances of which are unique. At the start of the twentieth century Brentano, for

instance, argued in response to Hering that green is phenomenally composed of

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yellow and blue (see Author for further discussion). More recently, the physicist Jan

Koenderink has suggested on phenomenological grounds that there might actually be

six basic hues: the Hering primaries plus cyan and magenta (2010: 579-81).15

Whatever the explanation of the relative ease and consistency with which some

trained subjects are able to make judgments about the proportions of hues a stimulus

contains, it needs to be consistent with ignorance, error, and variation amongst

normal perceivers who possess a full range of colour concepts. At the very least, the

existence of ignorance, error, and variation calls into question the view that colour

appearance judgments are simply a matter of ‘reading off’ the contents of perceptual

experiences.

This concern is made more pressing by the fact that Byrne and Hilbert’s

explanation of colour appearance judgments is not the only available one. A

competing explanation is suggested by a description of the judgments used in the

Natural Colour System by one of its principal proponents, Lars Sivik:

As references for [estimation and identification of colors] we are able, according to

Hering, to use the built-in images that we all have of ideal yellow, red, blue, green, white,

and black. The phenomenological basis of Hering’s postulates, to which we all have

access, is that all colors can be described in terms of resemblances to these six elementary colors…The

phenomenological-empirical basis for the NCS is thus that all colors (here I refer to

percepts of surface colors) more or less resemble these elementary colors….The unit of

measurement chosen for the variable “visual resemblance to the elementary color A” was

percent (1997: 174-175).

The view that this suggests is reminiscent of a view expressed by Hume:

It is evident, that even different simple ideas may have a similarity or resemblance to

each other; nor is it necessary, that the point of circumstance of resemblance should be

distinct or separable from that in which they differ. Blue and green are different simple

ideas, but are more resembling than blue or scarlet; though their perfect simplicity excludes

all possibility of separation or distinction (1739-40: 1.1.7)

According to the alternative account that these remarks suggests, orange objects

(for example) are both reddish and yellowish because orange things are like, to a

certain degree, both unique red and unique yellow things. But the resemblance of

orange to red and yellow is not to be further explained in terms of anything else. It is

15 According to Koenderink ‘I fail to see RED and BLUE in a PURE PURPLE, just as I fail to see RED and

GREEN in a PURE YELLOW’ (2010: 579). He argues further that the six basic hue model captures

alterations of brightness amongst the hues (that yellow, cyan, and magenta are relatively bright, and

red, green, and blue relatively dark), and allows for the basic hues to equally spaced around the colour

circle.

13

not to be explained in terms of orange objects sharing properties with red and yellow

objects: as, for instance, on Byrne and Hilbert’s (1997) earlier suggestion that orange is

similar to red because both have the coarse-grained determinable property of being

reddish. Nor is it to be explained in terms of orange and red objects being represented

as having different proportions of the hue magnitude R. Instead, the similarity is

basic: it is simply the case that orange objects are like, to different degrees, unique

yellow and unique red objects. From this perspective, when Byrne asks ‘The peach

and raspberry, one might think, don’t seem to share a color property. So how come

they look similar?’ (2003: 656), the call for explanation is misplaced.

This view still needs to explain the phenomenon that Byrne and Hilbert use to

motivate the appeal to hue magnitudes: some trained subjects’ abilities to make

relatively reliable judgments about colour appearance. Sivik’s suggestion is that we

have ‘built-in images’ of pure instances of the Hering primaries that we are able to

mentally compare presented samples with, and on this basis make judgments about

the relative degrees to which a presented sample resembles those built-in images.16

This might seem suggestive of what Wittgenstein describes as a ‘false picture’ of

recognition:

as if recognizing always consisted in comparing two impressions with one another. It is as

if I carried a picture of an object with me and used it to perform an identification of an

object as the one presented by the picture (1953: §604).

An alternative, in keeping with the basic thought that colour similarities are basic, is

that we employ recognitional capacities to make judgments about a sample’s degree of

resemblance to pure instances of the elementary colours, without explicitly needing to

bring images of these colours to mind (see e.g. Evans 1982 on recognitional

capacities,). Either way, judgments about colour appearance would go beyond what is

strictly speaking presented in experience, or at best constitute a form of ‘seeing as’ (see

e.g. Wittgenstein 1953, and Brewer 2011: §5.3 for one way of developing this idea).

As well as explaining how subjects are able to make colour appearance

judgments, this account also has the scope to explain how ignorance, error, and

variation are possible. Rather than simply ‘reading off’ information about colour

appearance from the content of experience, judgments about similarity relations are

only possible if these similarity relations are salient, and making these similarity

relations salient might require prompting—just as one person’s similarity to another

might only be noticed if you are prompted to direct your attention in the appropriate

16 Compare Shamey et al (2011) who conclude that ‘The above finding supports that uHs [unique hues] are a well established concept in the minds of subjects that have not had extensive exposure to the idea’. Describing these ‘cognitive references’ as ‘built-in’ suggests that they are innate; a slight variation on this would be to hold that they are learnt through experience.

14

ways, or images of the two people are placed side by side. Likewise, making judgments

about similarity relations involves making judgments about the resemblance of

samples to certain fixed points in colour space, but which points in colour space are

taken to be the fixed points is not simply determined by the content of the experience,

and might be something about which disagreement is possible—just as some people

are able to see resemblances between people that others cannot.17

The significance of this alternative account is that it provides some support for

the claim that colour similarity relations are, contrary to what Byrne and Hilbert

suggest, genuine (or natural) relations of similarity. Genuine similarity relations contrast

with relative similarity relations, which hold between things that are similar only

relative to a specific property or properties: for instance, in the way that squares and

triangles are similar relative to the properties of being geometrical shapes, having more than

three sides, being examples of relative similarity used by Byrne and Hilbert (1997: 274). Genuine

similarity relations are not relative in this way, and hold between things in virtue of

their intrinsic or essential natures: for instance, in the way that you might think that a

cube is more similar to a pentagon than a circle (cf. Byrne and Hilbert 1997: 274-275).

Byrne and Hilbert are keen to avoid the suggestion that the similarity relations

between the colours are genuine similarity relations, because the SSR types with

which they identify colours do not stand in similarity relations that are genuinely

similar, but at best stand in relations of relative similarity (Byrne 2003: 648; Byrne and

Hilbert 2003: 13). However, if the similarities between the colours are represented as

basic, then this provides a reason for thinking that colour similarity relations are

genuine similarity relations.

Of course, it might be suggested that it does not follow from the fact that

colour similarity relations are represented as being genuine similarity relations that they

are genuine similarity relations: colours might be relatively similar even if they are not

represented as such. There would at least be a tension for physicalists who deny

premiss (2) of the Argument from Structure in pursing this line of response. The initial

motivation for denying premiss (2) of the Argument from Structure (rather than

premiss (1)) was to be faithful to the appearances. But if we should prefer an account

of the structural properties of the colours according to which they are as they appear,

then we should prefer an account according to which they are genuine (rather than

relative) similarity relations if this is how they are represented. Nevertheless, Byrne

and Hilbert’s account is primarily an account about the nature of the colours, and it

might be suggested that their account of the way colours are represented is ultimately

dispensable. The more important question at this point is therefore whether Byrne 17 Compare Mizrahi (2009). Mizrahi defends a form of conventionalism about the unique/binary

distinction. However, the view that perceiving similarities between the colours involves a form of

‘seeing as’ does not entail conventionalism, if certain ways of seeing colours are privileged.

15

and Hilbert’s account of the structural properties of the colours is empirically

adequate.

3.3 Is Byrne and Hilbert’s Account Empirically Adequate?

Turning from the way colours are represented to the properties that the colours are

identified with, a key question is whether there are perceptual similarities between the

colours that are not preserved at the level of reflectance-types. One problem in this

respect are similarity relations between the unique hues themselves.

NCS colour space represents the four unique hues at the cardinal compass

points of the hue circle, to emphasise their psychological salience. However, the NCS

strictly speaking consists of four independent scales—red-yellow, yellow-green, green-

blue, blue-red—rather than one single dimension of hue.18 As such, it is not possible to

compare the end points of these scales themselves. This feature is reflected in Byrne

and Hilbert’s account. Because the unique hues are all represented as having 100% of

one of the four magnitudes (and therefore have no hue magnitudes in common), no

comparative judgments of similarity between the unique hues are themselves possible;

correlatively, there are no similarity relations between the reflectance-types with

which Byrne and Hilbert identify the unique colours.

This is problematic given that the unique hues themselves appear to stand in

asymmetric similarity relations (cf. Hardin 1993: 127-134).19 A number of

representations of colour space locate the unique hues at irregular points around the

hue circle. In Munsell colour space, for instance, the hue circle is divided into 100

perceptually equals steps (judged at the level of just noticeable differences), and

partitioned into five basic hue groups: the four elementary hues identified by Hering—

red, yellow, green, and blue—plus purple. The reason for this is that the number of

perceptually equal hue steps between the between the unique instances of Hering’s

elementary hues in the Munsell system varies considerably: from red to yellow it is 23,

from yellow to green it is 18, from green to blue it is 28, and from blue to red it is 31.

Purple is identified as an elementary Munsell hue so that the elementary hues can be

equally spaced around the perimeter of the hue circle.

The samples in the Munsell colour atlas are spaced according to colorimetric

rules of additive colour mixture using photometers and Maxwell disks, rather than

direct visual observation. As a result, multi-dimensional scaling (MDS) studies on the

Munsell system of colour classification have since revealed slight anomalies: for

18 As Sivik remarks describing the decision to arrange the hues ordered by the NCS around a circle,

rather than a square: ‘since the hue circle is such a well established concept, everybody yielded to this

convention. One should, however, be aware of the fact that the hue circle is conceptually not one scale

but four’ (Sivik 1997: 176) 19 This is noted as a potential problem by Byrne (1993: 661, n. 40) but no attempt is made to address it.

16

instance, colours between Munsell-Blue (‘5B’) and Munsell-Purple-Blue (‘5PB’) look

comparatively too similar to each other. Still, these MDS studies vindicate Munsell’s

basic partition of the hue circle into five, a feature preserved in the isotropic Optical

Society of America (OSA) colour space, for instance, which unlike the Munsell system

does give a strict preference to colour appearances over psychophysical data (Indow

1988: 463; Jameson and d’Andrade 1997: 299-301).

Consistent with this, Kuehni (2005) found that the distances between the mean

values for Munsell chips identified as unique varies across the unique hues. The

distance between the mean hues identified as unique green and unique blue was

approximately 8.5 Munsell hue steps. It was about the same between unique yellow

and unique red—although Kuehni reports having the impression that the mean green

and blue chips were more similar to each other than the mean yellow and red chips.

However, it was approximately 10 hue steps between the mean values for unique

yellow and unique green, and approximately 13 hue steps between unique blue and

unique red. (Compare Hume’s claim above that ‘Blue and green are different simple

ideas, but are more resembling than blue or scarlet’.)

So, not only is it questionable whether objects are represented as coloured in

virtue of being represented as having proportions of hue-magnitudes, but more

importantly Byrne and Hilbert fail to account for all the relevant relations of similarity

between the colours. As such, there are serious problems with the response to the

Argument from Structure.

4. Premiss (2): Naïve Realism

The previous sections motivated the claim that the structural properties are essential

properties of the colours, and argued that so understood a prominent form of

reductive physicalism is unable to adequately account for them. This section outlines

an alternative response to the Argument from Structure that, like the form of

reflectance physicalism considered in the previous section, denies premiss (2).

The Argument from Structure is directed in the first instance at reductive forms

of colour physicalism, according to which colours are ‘narrowly’ physical properties:

properties described by the physical sciences, such as surface spectral reflectances or

their micro-physical realisers. This argument is in turn often used to motivate one of a

range of broadly subjectivist theories of colour: forms of eliminativism according to

which things in the environment are not coloured at all (e.g. Hardin 1993; Maund

1995; Pautz 2006), or forms of relationalism according to which colours are relational

properties constituted in terms of perceiving subjects (e.g. Thompson 1995). However,

without further argument it doesn’t follow from the fact that there are no narrowly

physical properties of things in the environment that instantiate the structural

properties standardly attributed to the colours, that there are there are no physical

17

properties in a more inclusive sense of the word ‘physical’ that instantiate the

structural properties characteristic of the colours.

Naïve realist theories of colour (sometimes also called primitivist theories of

colour) agree with reductive physicalist theories of colour that colours are mind-

independent properties of things in the environment: properties of things whose nature

and existence is constitutively independent of conscious subjects.20 They differ from

reductive physicalist theories in maintaining that colours are superficial (or sui generis)

properties: they are properties that are not described by the physical sciences. But to

say that colours are superficial properties is not to say that there is no sense in which

colours are ‘physical’. First, colours as the naïve realist conceives of them are ‘physical’

in an undemanding, non-technical, sense of ‘physical’ according to which tables,

chairs, galaxies, people and the like are all ‘physical things’—in contrast, for instance,

to sensations, ghosts, or souls (cf. Stroud 2000: Chapter 3). Second, colours as the

naïve realist conceives of them are typically also ‘physical’ in the more technical sense

that they are normally taken to supervene on narrowly physical properties like surface

reflectance profiles. To say that the colours supervene on narrowly physical properties

is to say that there can be no difference in an object’s colour without a difference in its

narrowly physical properties. Supervenience can come in different strengths

depending, for example, on whether there can be no difference in an object’s colour

without a difference in its narrowly physical properties as a matter of nomological

necessity, or whether there can be no difference in an object’s colour without a

difference in its narrowly physical properties as a matter of metaphysical necessity.

Either way, supervenience promises a way of integrating higher-level properties like

colours into a broadly naturalistic framework, without simply identifying these higher-

level properties with narrowly physical properties: the higher-level properties depend

on, without being identical to, the underlying physical properties of objects. To say

that colours are superficial properties that are distinct from, but supervene on,

narrowly physical properties is therefore not to express a commitment to a form of

anti-physicalism, but just to reject forms of reductive physicalism. In this respect, naïve

realist theories of colour are equivalent to non-reductive physicalist theories of mind.21

Naïve realist theories provide a different way of responding to the Argument

from Structure; alternatively, the Argument from Structure can be understood as a

20 Primitivism is sometimes characterised as a view that comes in realist and eliminativist forms,

depending on whether colours are primitive properties that physical objects (actually) instantiate (e.g.

Pautz 2006). As I understand it, naïve realism is not neutral in this respect. For further discussion, see

e.g. Author. 21 Naïve realist theories of colour have become increasingly popular in recent years. Proponents include

Campbell (1993), Yablo (1995), Watkins (2010), and Dorsch (2010). For discussion, see Byrne and

Hilbert (2007).

18

way of motivating a naïve realist theory of colour.22 According to the naïve realist,

colours are superficial properties of things in our environment, and they instantiate

just those structural properties that they are perceived to. These structural properties

are, as they are often taken to be, essential properties of the colours, and the colours

themselves are those properties from which our colour experiences inherit their

phenomenal character. As such, the naïve realist theory provides a straight-forward

account of the structural properties of the colours.

Whether this is a viable account of the structural properties of the colours will

depend on the viability of the naïve realist theory of colour more generally. It is often

assumed that modern science has ‘shown’ that naïve realist theories of colour are

mistaken. I therefore want to conclude by briefly considering two ways that this

general line of argument against the naïve realist can be developed and resisted.23

One line of objection to the naïve realist theory of colour is an instance of the

more general ‘causal exclusion problem’ familiar from discussions of mental

causation. According to this line of argument, if colours were superficial mind-

independent properties, then they would be excluded from playing any causal role in

the production of colour experiences by an object’s narrowly physical properties, and

so there would be no reason to believe in their existence (e.g. Hardin 1993: 61;

Johnston 1992: 139; Jackson 1996). Detailed consideration of this argument lies

beyond the scope of this paper, but there are nevertheless a number of general reasons

for thinking that it is unconvincing. First, the argument threatens to over-generalise.

Worries about causal exclusion are not unique to naïve realist theories of colour, but

also arise for the dispositionalist and the reflectance physicalist: dispositional

properties threaten to be causally excluded by their physical grounds, and types of

reflectance profile not only threaten to be causally excluded by their tokens, but are

anyway relatively high-level physical properties that threaten to be causally excluded

by microphysical properties of objects (e.g. Byrne and Hilbert 2007: 84). The only

view left standing by this line of argument appears to be the view that colours are

22 Compare Dorsch (2010). Pautz (2006) uses the Argument from Structure to motivate a form of

eliminativist primitivism. However, Pautz’s eliminativism does not sit easily with the ‘Relational View’

of colour experience that he uses to motivate primitivism, according to which ‘the structural properties

of colours are simply inherited from (or amount to) the structural properties of the colours that we are

sensorily related to in having those colour experiences’ (2006: 543; see also §2 above). The most natural

interpretation of the Relational View is that the properties of objects that we are sensorily related to in

perception are actually instantiated by those objects. In denying this, Pautz appears to accept an error

theory of the general kind that he is otherwise keen to avoid. 23 A different line of objection focuses on the claim that colours are mind-independent, which

represents common ground between the naïve realist and the reductive physicalist. I consider attempts

to undermine this claim by appealing to variations in perceptual experience elsewhere (Author).

19

micro-physical properties of objects, and the sheer strength of this conclusion might

seem to be suggestive of a problem with the argument rather than a reason to

embrace its conclusion. Second, and more positively, insofar as naïve realism is a form

of non-reductive physicalism, naïve realists can co-opt any one of a variety of

responses by non-reductive physicalists to parallel concerns about the causal exclusion

of mental states by their physical realisers (e.g. Campbell 1993; Yablo 1995; Watkins

2010).

A second line of objection is more closely connected to the issues discussed in

this paper, and concerns the seemingly close connection between the way colours

appear and the nature of our perceptual processing mechanisms. There might be

seem to be a deep tension, if not an outright incompatibility, between acknowledging

the close connection between the way our perceptual processing mechanisms function

and the way colours appear on the one hand, and the view that the structural

properties of the colours are essential properties of mind-independent entities on the

other. As Hardin, for instance, trenchantly puts the point:

so much about the colors—particularly the division between unique and binary hues—is

manifestly bound up with the peculiar characteristics of the human visual system that it

seems a vain pursuit indeed to search for a parallel set of structures in the general order

of nature. One might as well set about earnestly constructing improved Ptolemaic

epicycles (1993: 67).

In this respect, it might seem that anything other than a broadly subjectivist theory of

colour—or at any rate, one that acknowledges the subject’s contribution to the

phenomenal character of experience (like the view discussed in §2)—is inconsistent

with what scientific investigation has revealed about the how our visual processing

mechanisms function.

The fundamental problem with this line of argument, however, is that it

doesn’t follow from the fact that the way colours are perceived depends on the way

our visual processing mechanisms function, that the nature and occurrence of colour

experiences can thereby be explained solely in terms of those mechanisms. After all,

the way that we perceive anything depends upon the way that our visual processing

mechanisms function, and it does not obviously follow from this that all perceptual

experiences can be explained solely in terms of those mechanisms, without any

reference to the objects, properties, and relations in the perceiver’s environment that

those experiences purport to be experiences of. An alternative way of thinking of the

visual processing mechanisms is to think of them as enabling conditions that make

possible the perception of colours. So understood, explanations of the phenomenal

character of colour experiences in terms of the way visual processing mechanisms

function do not exclude explanations of the phenomenal character of colour

20

experiences that appeal to the properties of objects; rather they presuppose them. As

Kalderon, for instance, puts it:

Let us grant that the spectral power distribution of the light reaching the perceiver’s eye

and its retinal effects, as well as the subsequent, cascading effects of further visual

processing, at least partly determine the phenomenal character of the perceiver’s colour

experience. However, they do so, in part, by determining the fact that the appropriately

situated perceiver stands in the relevant relation to the qualitative aspect of the colour

presented (2011: 257).

5. Conclusion

Accounting for the structural properties of the colours provides a widely discussed

problem for physicalist theories of colour. This paper has raised some objections to a

prominent reductive physicalist attempt to account for the structural properties, and

outlined an alternative form of non-reductive physicalism: a naïve realist theory of

colour according to which colours are superficial mind-independent properties. I have

argued that this alternative approach allows us to take the chromatic appearances at

face value, without ignoring or denying the scientific facts about the causal processes

underlying colour perception.24

Bibliography

Abramov, I. (1997) Physiological mechanisms of color vision. In C.L. Hardin

and L. Maffi (eds) Color categories in thought and language (pp. 89-117).

Cambridge: Cambridge University Press.

Berkeley, G. (1713/1734). Three dialogues between Hylas and Philonous. In M.

Ayers (ed) Philosophical works. London: Everyman.

Boghossian, P. and Velleman, D. (1991). Physicalist theories of colour. Philosophical

Review 100: 67-106.

Brewer, B. (2011). Perception and its objects. Oxford: Oxford University Press.

Byrne, A. (2003). Color and similarity. Philosophy and Phenomenological Research,

66(3): 641-665.

⎯ (2005). Perception and conceptual content. In E. Sosa and M. Steup (eds)

Contemporary Debates in Epistemology. Oxford: Blackwell.

Byrne, A. and Hilbert, D. (1997). Colors and reflectances. In A. Byrne and D. Hilbert

(eds) Readings on color: The philosophy of color (pp 263-288). Cambridge,

Mass.: MIT Press.

⎯ (2003). Color realism and color science. Behavioural and Brain Sciences 26: 3-

21.

24 Acknowledgements

21

⎯ (2007). Color primitivism. Erkenntnis 66: 73-105.

Campbell, J. (1993). A simple view of colour. In J. Haldane and C. Wright (eds)

Reality, Representation, and Projection. Oxford: Oxford University Press.

Cohen, J. (2003). On the structural properties of the colors. Australasian Journal of

Philosophy 81(1): 78-95.

⎯ (2009). The red and the real. Oxford: Oxford University Press.

Chirimuuta, M. (2011). Touchy-feely colour. In Biggam, Hough and Simmons

(eds) New directions in colour studies. Amsterdam and Philadelphia: John

Benjamins.

Churchland, P. (2007). On the reality (and diversity) of objective colors: How color-

qualia space is a map of reflectance-profile space. Philosophy of Science 74:

119-149.

Davies, W. 2014. The inscrutability of colour similarity. Philosophical Studies 171(2):

289-311.

Degenaar, J. and Myin, E. (2014). The structure of color experience and the existence

of surface colors. Philosophical Psychology 27(3): 384-400.

De Valois, R.L., & De Valois, KK. (1993). A multi-stage color model. Vision

Research 33(8): 1053-1065.

Dorsch, F. (2010). Colour realism and colour resemblance. Rivista di Estetica 43:

85-108.

Evans, G. (1982). Varieties of reference. Oxford: Clarendon Press.

Fuld, K., J. Werner and B. Wooten. (1983). The possible elemental nature of

brown. Vision Research 23: 631-7.

Fine, K. (1994). Essence and modality. Philosophical Perspectives 8: 1-16.

Hård, A., Sivik, L., and Tonnquist, G. (1996). NCS, Natural Color System—From

concept to research and applications, parts 1 and 2. Color Research and

Application 21: 180-220.

Hardin, C.L. (1993). Color for philosophers. Indianapolis: Hackett.

Hering, E. (1920). Outlines of a theory of the light sense. Translated by L. M. Hurvich

and D. Jameson. Cambridge, MA: Harvard University Press, 1964.

Hume, D. 1739-40. A treatise of human nature. Edited by D.F. Norton and M.J.

Norton. Oxford: Oxford University Press, 2000.

Indow, T. (1988). Multidimensional studies of Munsell solid. Psychological Review

95(4): 456-470.

Jackson, F. (1996). The primary quality view of color. Philosophical Perspectives 10:

199-219.

Jameson, K. and D’Andrade, R.G. (1997). Its not really red, green, yellow, blue: An

inquiry into perceptual color space. In C.L. Hardin and L. Maffi (eds) Color

categories in thought and language (pp. 295-319). Cambridge: Cambridge

22

University Press.

Johnston, M. (1992). How to speak of the colors. Philosophical Studies 68: 221-63.

Jraissati, Y. (2014). Proving universalism wrong does not prove relativism right:

Considerations on the ongoing color categorization debate. Philosophical

Psychology 27(3): 401-424.

Kalderon, M. (2011). The multiply qualitative. Mind 120: 239-262.

Koenderink, J. (2010). Color for the sciences. Cambridge, Mass.: MIT Press.

Kuehni, R. (2005). Focal color variability and unique hue stimulus variability. Journal

of Cognition and Culture 5: 387: 407.

Lewis, D. (1997). Naming the colors. Australasian Journal of Philosophy 75(3): 325-

342.

Locke, J. (1690). An essay concerning human understanding. Oxford: Oxford

University Press, 1975.

Matthen, M. (2005). Seeing, doing, and knowing. Oxford: Oxford University Press.

Maund, B. (1995). Colours: Their nature and representation. Cambridge: Cambridge

University Press.

McLaughlin, B. (2003). Color, consciousness, and color consciousness. In Q. Smith

and A. Jokic (eds) Consciousness: New philosophical perspectives (pp 97-154).

New York: Oxford University Press.

Mizrahi, V. (2009). Is colour composition phenomenal? In D. Skusevich and P.

Matikas (eds) Color perception: Physiology, processes and analysis (pp. 185-

202). New York: Nova Science Publishers.

Pautz, A. (2006). Can the physicalist explain colour structure in terms of colour

experience? Australasian Journal of Philosophy 84(4): 535-564.

Roberts, P., Andow, J., and Schmidtke, K. (Forthcoming). Colour relationalism and

the real deliverances of introspection. Erkenntnis.

Saunders, B., and van Brakel, J. (1997). Are there non-trivial constraints on color

categorisation? Behavioural and Brain Sciences 20: 167-232.

Schroer, R. (2010). Where’s the beef? Phenomenal concepts as both demonstrative

and substantial. Australasian Journal of Philosophy 88(3): 505-522.

Sivik, L. (1997). Color systems for cognitive research. In C.L. Hardin and L.

Maffi (eds) Color categories in thought and language (pp. 163-193).

Cambridge: Cambridge University Press.

Shamey, R., Sedito, M., and Kuehni, R. (2010). Comparison of unique hue stimuli

determined by two different methods using Munsell color chips. Color

Research and Application 35(6): 419-424.

Shamey, R., Shepherd, S., Abed, M., Chargualaf, M., Garner, N., Dippel, N.,

23

Weisner, N., and Kuehni, R. (2011). How well are color components of

samples of the Natural Color System estimated? Journal of the Optical Society

of America A 28(10): 1962-1969.

Shoemaker, S. (2003). Content, character, and color. Philosophical Issues 13: 253-

278.

Stroud, B. (2000). The quest for reality. Oxford: Oxford University Press.

Sundström, P. (2013). Are colours visually complex? In C. Svennerlind, J. Almäng

and R. Ingthorsson (eds) Johanssonian Investigations: Essays in Honour of

Ingvar Johansson on His Seventieth Birthday (pp. 627-639). Frankfurt: Ontos

Verlag.

Thompson, E. (1995). Colour vision: A study in cognitive science and the philosophy

of perception. London: Routledge.

Tye, M. (2000). Consciousness, color, and content. Cambridge, Mass.: MIT Press.

Watkins, M. (2010). A posteriori primitivism. Philosophical Studies 150(1): 123-137.

Wittgenstein, L. (1953). Philosophical investigations. Oxford: Blackwell.

Yablo, S. (1995). Singling out properties. Philosophical Perspectives 9: 477-502.