From Towards a Science of Consciousness 3                                        CogNet Proceedings

II.     Color -- Introduction

David J. Chalmers

Color experience is a microcosm of consciousness. In particular, many of the deepest philosophical questions about consciousness can be vividly illustrated in the case of consciousness. Why do experiences of red and blue have the particular subjective qualities (or qualia) that they do? Jackson (1982) has argued that a neuroscientist with black-and-white vision might know all the physical facts about color processing in the brain and in the world, but would still not know what it is like to have a red experience. If so, it seems that there might be a deep explanatory gap between knowledge of physical facts and knowledge of qualia.

Another traditional philosophical problem about color is the problem of the inverted spectrum. At some point in our lives, many of us have entertained the hypothesis that when others look at red objects, they have the sort of experience that we have when we look at blue objects. It might be argued that this would be undetectable, since we will call our different experiences by the same names ("red" or "blue"), associate them to the same objects, and so on. Even if one thinks it unlikely that such cases actually exist, the mere logical possibility of such cases raises questions about whether we can explain facts about color experience in terms of facts about processing.

In this section, three theorists of color apply empirical results from the science of color to these ancient philosophical problems. Much is known about color processing now that was not known a few decades ago, and some of these results are highly relevant to the philosophical debate. In this way we see how science and philosophy can interact productively, with benefits for both sides.

Stephen Palmer discusses ways in which the idea of a behaviorally undetectable inversion of color experience may or may not make sense. The most obvious ways to understand an inverted spectrum turn out to be deeply problematic, since they will violate certain asymmetries in the space of colors. But certain inversions involving the red-green dimension may hold promise, though this is affected in turn by questions about basic color terms in human culture. Palmer goes on to draw a general moral for the science of consciousness, proposing an "isomorphism constraint" relating processing to experience. Processing facts can characterize the abstract strucure of the space of color qualia, but they may not be able to tell us about the underlying qualia themselves.

C. L. Hardin is more skeptical about the idea of a spectrum inversion. He argues that once we truly understand all the facts about the structure of color space, the idea of an inversion will not make sense even as a logical possibility: color structure tells us all there is to know about color qualia. He discusses a number of deep asymmetries in color space, drawn from work in both anthropology and psychophysics, which he argues rule out any possible inversion. Hardin suggests that this sort of result has the promise of closing the explanatory gap between physical processes and color experiences.

Martine Nida-Rumelin discusses the intriguing possibility that there may be some actual cases of spectrum inversion. It turns out that there is a theoretical possibility that some subjects (about 1 in 700 males) have two forms of colorblindness simultaneously, which would switch the responses of the cones in the retina, plausibly resulting in a systematic transposition in their color space. Nida-Rumelin discusses philosophical consequences of this "pseudonormal vision," and goes on to address the arguments given by Hardin. She argues that even if complete qualia inversions are impossible, this leaves the explanatory gap between physical processes and color qualia intact.

Further philosophical and scientific papers on color can be found in the two-volume anthology edited by Byrne and Hilbert (1997).


Byrne, A., and D. R. Hilbert. 1997. Readings on Color. (Volume 1: The Philosophy of Color. Volume 2: The Science of Color). MIT Press.

Jackson, F. 1982. Epiphenomenal qualia. In Philosophical Quarterly 32:127136.