...wherein we get a taste of what it is like to philosophize about color. In particular, we consider physicalism about color, as opposed to Eliminativism or Conventionalism. Our guiding background theory is representationalism:
What must colors be for them to be represented in our colored experiences? We assume that propositions--bearers of truth/falsity--are extractable from perceptual experiences in general: that "the proposition that *there is a red bulgy object on the table* is part of a subject's experience" when he looks at a red tomato (5). We assume that colors are represented in experience so conceived, and ask what colors must be for this to be possible.
What are the alternatives to Physicalism about color? Eliminativism: there ain't no colors. Dispositionalism: colors are psychological dispositions. To dispositionalism we pose "Berkeley's Challenge": why be dispositionalist about color and not dispositionalist about every other property (shape, size, etc.) that we can detect through the senses? (or more generally, that we can detect at all?) There are, of course, some things to say here---colors are only detectable via one sense-modality, physicalist explanations of phenomena that don't involve humans/animals rarely mention color, etc., but we set those aside for now. Primitivism: colors are not physicalist, not dispositionalist, and not nothing. Finally, Physicalism, which B&H endorse, identifies color with some physical property of (colored) objects. As they see it there are two main (related) objections to physicalism: physicalism cannot account for "the structure of phenomenal space" (they cite Boghossian and Velleman for this point), and, more particularly, that physicalism cannot account for the "opponent-process theory of vision", which presents several generalizations of which colors humans perceive in terms of the relative degrees of stimulation of their short-, medium-, and long-wavelength photoreceptors.
The first incarnation of physicalism is that colors are reflectance properties. A reflectance property for a given (uniformly colored) object is given as a graph with percentages from 0-100 on the y-axis and wavelengths on the x-axis. The height of the graph at a particular value of x indicates what proportion of incident light of wavelength x is reflected by the object. It appears that this is the best candidate for something which is both a physical property and a property to which we are sensitive in our color vision.
Three objections are raised: the first has to do with "metamers." These are pairs of objects whose reflectance graphs look very different but whose perceived colors are the same (the objects are indistinguishable under normal light.) B&H note that they will have to bundle different reflectance properties together to define *determinable* (as opposed to determinate) colors together anyway, so there is no objection in principle to identifying colors with sets of reflectance properties. These sets might not be, in any sense, "natural":
"Surfaces with grossly different reflectances can perceptually match even under fairly normal illuminants....so the reflectance-types that we identify with the colors will be quite uninteresting from the point of view of physics or any other branch of science unconcerned with the reactions of human perceivers. This fact does not, however, imply that these categories are unreal or somehow subjective. (11)"
...I take it this is a somewhat significant cost, since it seems that an account of colors in these terms would suggest that our color-concepts are highly gerrymandered. But perhaps this is the best we can do.
We then have a brief (quarantined) digression on transparent objects and colored lights. The authors suggest we shift to what they call "productance" (a sum of light reflected and light emitted) to account for these. They stress that although productance is relative to illumnants, the property productance enters into (the candidate property to be identified with color) is independent of any particular illuminant. There is also a somewhat shocking aside about so-called "related" and "unrelated" colors: related colors are only perceived when there are certain other colors in the scene. Apparently brown is such a color. I don't really understand B&H's reply, but it's got something to do with the fact that the perception of color constancy apparently relies a lot on the colors of other perceived objects in the environment.
On to the objection from phenomenal structure. Among the things to be explained are the distinction between binary hues (hues experienced as proportions of different colors--e.g. orange) and unique hues (e.g. red), as well as the opponent structure of the colors (green-red, yellow-blue, etc.) To respond to this challenge, B&H invoke the representational content of color-experiences:
"such heroism [the attempt to reject the explanatory demand from phenomenal structure] is not required. In our view, the phenomena of color similarity and opponency show us something important about the *representational content* of color experience--about the way the color properties are encoded by our visual systems And once we have a basic account of the content of color experience on the table, it will be apparent that there is no problem here for physicalism. (13)"
We complicate the picture--not the picture of color, as far as I can tell, but the picture of the content of color experiences. Before, experiences with "color content", given that color x is the physical property F, were simply of the form "a is F." Revised thesis: experience represent "objects as having proportions of hue-magnitudes." [NB here hue = color, in the physicalist sense defined and defended above.] So, for example, where F and G are primary hues, our experience tells us something like "a is both F and G, and it is twice as F as it is G."
Is there a cheat here? We started out wanting to account for e.g. the opponency of colors in terms of features of the colors themselves; instead, we wound up giving an account of the opponency of colors in terms of the content of a color-experience. Comparison: we could account for the "additive opponency" of certain pairs of integers (like 2 and -2) in terms of features of the numbers themselves---presumably this is what we do. Or we could give an account of the additive opponency of the pairs in terms of our experience. (I'm not sure what this would come to in the case of numbers.) Nothing can appear both squat and thin, since squatness consists in being wider than one is tall and thinness consists in being taller than one is wide; given this, we can account for the "opponency" of experiences of squat objects and experiences of thin objects by saying that squatness is the property of being wider than one is tall, and thinness is the property of being taller than one is wide. Moreover, we seem to have backed away from suggesting that we can actually detect reflectance properties---rather, we can merely detect relative ratios of reflectance properties. (Compare: we can actually perceive width and height and calculate squatness from these two things, or: we can only perceive the presence or absence of squatness.) This thought seems to be behind H&B's discussion of the lengths of sticks (14).
We now revisit several other objections to physicalism. The first comes from variation amongst color-perceiving subjects: which objects are perceived as "unique green" or balanced orange (a hue exactly as red as it is yellow) vary from subject to subject, often by a margin which is quite large relative to any individual subject. This fact leads some philosophers (or psychologists?--someone named Hardin) to espouse a kind of "conventionalism" about green: in the absence of consensus about which hue chip is unique green, "the question..can be answered only by convention (17)." Hardin is also an eliminativist, and his two thoughts seem connected here (although at first blush they are inconsistent--how can we just pick one when the real answer is "none"?) If the suggestion is that we must espouse an error theory about unique green (given the variation amongst color-perceivers, any choice of a hue chip as the real unique green will make a majority of perceivers wrong), and this error theory is unacceptable (it would be better to espouse eliminativism about colors), then the authors' response is simply that an error theory is not really so disastrous. They remind us that we are speaking of determinate rather than determinable properties. (We are not espousing an error theory for green---only for unique green.) They also remind us that we are not ready to espouse eliminativism about a host of other properties which are often perceived inaccurately (they use the example of spatial properties which are commonly misperceived by people with slightly mismatched retinal images across their two eyes.)
A host of responses that make reference to the peculiarity of the case of color: color is not detectable via other sense-modalities (if we are in error visually we cannot use other senses as independent checks--this distinguishes color from spatial properties). Secondly, color properties, if they exist, do not enter into any "data or theories of any sciences other than those concerned with animal behavior" (e.g., they only enter into intentional explanations--again, unlike spatial properties). So there seems to be a *more* significant cost to espousing an error theory for a color-property (and if physicalists are right, unique green *is* a color-property) than one of these other properties. Unique green will *not* enter in to very many intentional explanations--in the usual way, at least--if most perceivers are in error about which objects are unique green. (We could substitute *a belief that something is unique green* in our explanations of their behavior, but then, since the belief that A is F does not in general entail the existence of a real property F, we could do just as well without it.) (17). B&H's response seems to be this: in order to save the phenomena of ordinary perceivers, we need green to be a really existing property. But if green is a really existing property, then unique green exists.
(The response is a sort of "supertruth" response: on each acceptable adjudication of the boundaries of green [corresponding to each slightly different perceiver], some hue chip is unique green. So it is supertrue that some hue chip is green even if it isn't supertrue *of* any particular hue-chip that *it* is unique green. The weaker thing is all we need to be realists about green and unique green.)
Finally, we revisit the inverted spectrum. H&B suggest that the inverted spectrum thought-experiment is basically irrelevant to the thesis of physicalism about color as they have presented it. Their presentation relied on representationalism about color-experience. This can be true even if (as proponents of inverted spectrum scenarios often think) "what it's like" to have an experience is not exhausted by the representational content of that experience. H&B do point out, though, that to the extent that a "phenomenist" (an opponent of representationalism/intentionalism qua thesis about how representational content *exhausts* phenomenal content) believes that features of color like opponency and the binary/unique distinctions are features of "what it's like", and that's not representational, he will give a different account of these features than the representationalist does.
