ABSTRACT
The initial stage of color perception-disregarding preretinal absorptionis photoreception. The spectral sensitivity envelopes of the photoreceptors are the primary determinant of color vision phenotype; postreceptoral processes can modify color vision, but they cannot produce it unless the spectral information has been captured in the photoreceptors. Photoreceptor spectral sensitivity in most chordates, humans included, is determined by the protein portion of the photopigment housed in photoreceptor membranes. The amino acid sequence of the protein, opsin, interacts with the chromophore, retinal, to tune the spectral sensitivity of the resultant visual photopigment. In humans, and in some other chordates, four genes affect photoreceptor spectral sensitivity.
