Color vision

Lore & Background

Color perception begins with specialized retinal cells called cone cells, which contain different forms of opsin with varying spectral sensitivities. Humans possess three types of cones—short (S), medium (M), and long (L)—resulting in trichromatic color vision. The cones do not correspond directly to specific colors; rather, color perception arises from complex processing in the retina and brain. In low light, vision is scotopic and mediated by rod cells, which are maximally sensitive near 500 nm and play little role in color vision. In brighter light, photopic vision uses cone cells, which are most sensitive near 555 nm.

Reader's Guide

Color vision is categorized by the dimensionality of the color gamut, which generally equals the number of photopsins expressed in vertebrates. The common vertebrate ancestor was tetrachromatic, but many lineages have lost photopsin genes. Two complementary theories explain color vision: the trichromatic theory (Young–Helmholtz) posits three cone types sensitive to blue, green, and red; the opponent process theory (Hering) describes antagonistic color pairs (red vs. green, blue vs. yellow, black vs. white). Both theories are widely accepted, though the opponent process theory has faced criticism, such as the after-image phenomenon showing cyan as the complement of red rather than green. Despite discrepancies, both remain influential in understanding color vision physiology.

Did You Know?

• The visible light spectrum ranges from about 380 to 740 nanometers.
• Humans cannot generally see infrared or ultraviolet wavelengths, but other animals may.
• The just-noticeable difference in wavelength varies from about 1 nm in blue-green and yellow to 10 nm or more in longer red and shorter blue wavelengths.
• The perception of 'white' can be formed by the entire visible spectrum or by mixing colors of just a few wavelengths.