The hypothesis that red-green "color blindness" is caused by alterations in the genes encoding red and green visual pigments has been tested and shown to be correct. Genomic DNA's from 25 males with various red-green color vision deficiencies were analyzed by Southern blot hybridization with the cloned red and green pigment genes as probes. The observed genotypes appear to result from unequal recombination or gene conversion (or both). Together with chromosome mapping experiments, these data identify each of the cloned human visual pigment genes.

Four color names-red, yellow, green, and blue-can be used singly or combined in pairs to describe all other colors. Orange, for example, can be described as a reddish yellow, cyan as a bluish green, and purple as a reddish blue. 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 yellow and blue).

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