Arthur Danto asserts in the foreword to C. L. Hardin’s Color for Philosophers that empirical science has shown us that something can be at once all-over red and all-over green. This is set against claims by David Pears, for example, that the denial of this is both true and a priori such that “anyone who began to look for exceptions would betray that he did not really understand the sentence.” Danto writes:
In the September 9, 1983, issue of Science, I read a paper with a title that ought to have been evidence that its authors did not understand their language, had Pears been right: “On Seeing Reddish Green and Yellowish Blue.” From the perspective of conceptual analysis, this would have been like coming across an article called “On Squaring the Circle and Duplicating the Cube.” One ought to have known, a priori, that the paper, if not merely jocular or arch, must be incoherent or false. Instead, the article in Science was informative and true, its title descriptively accurate, and it reported certain exceptions to the misclassified statement regarding red-green incompatibility, now seen to be a posteriori and admitting of exceptions. Its “Abstract” read as follows:
“Some dyadic color names (such as reddish green and bluish yellow) describe colors that are not normally realizable. By stabilizing the retinal image of the boundary between a pair of red and green stripes (or a pair of yellow and blue stripes), but not their outer edges, however, the entire region can be perceived simultaneously as both red and green (or blue and yellow).”
Under laboratory conditions specified in the body of the paper, observers reported that, among other alternatives, “the entire field appears to be a single unitary color composed of both red and green.” And against the background assumptions of philosophical analysis, this would be like inducing an experience of a single unitary plane figure composed of a circle and a square. (1988, xi-xii)
But, what is the thing that is at once all-over red and all-over green? What is the thing that is seen that is reddish green? Taking the abstract at face value, two colored things are presented to the subject, one red and one green; of course, (some) subjects report seeing reddish green in the region between them. Presumably the subjects are mistaken and the scientists (Crane and Piantanida) have simply shown us how to trick a subject into thinking that she sees something that is reddish green. After all, the region between the red and the green stripes is neither red nor green, nor is it reddish green. There doesn’t seem to be any reddish green thing to be seen. Unless, that is, we think that the subject saw something besides (some parts of) the stimulus — a reddish green sense datum, perhaps. If that is the correct way to understand the experiment, then it is evidence against Pears’s claim that no thing could be at once all-over red and all-over green; but, of course, the experiment does not establish that.
