Color-coded cells in goldfish, cat, and rhesus monkey.

JLhere are four recognized types of cell involved in color vision. Receptors absorb light over a restricted region of the visible spectrum, the wavelength of greatest sensitivity being different for different receptors, but the type of response (hyperpolarization) being the same for all wavelengths in all vertebrate receptors. Beyond the receptors, one finds opponent color cells which give one sign of response (depolarization or ON response) for some wavelengths and the opposite sign of response (hyperpolarization or OFF response) for other wavelengths. Some of these are single color opponent cells, where the response to a particular wavelength does not vary from one part of the receptive field to another, and some are double