Color Vision
Human color perception depends on three types of cone cells, each sensitive to different wavelengths. When one cone type is absent or altered, the experience of color changes dramatically. Paint on the canvas and see how your art looks through different eyes.
Trichromatic theory
The Young-Helmholtz trichromatic theory (1802/1850) proposes that color vision depends on three types of cone photoreceptors in the retina, each with a different spectral sensitivity. The S (short) cones peak near 420nm (blue), M (medium) cones near 530nm (green), and L (long) cones near 560nm (red). Every color we perceive is a combination of these three signals.
Opponent-process theory
Ewald Hering's opponent-process theory (1892) complements trichromacy by noting that the brain processes cone signals into opponent channels: red-green, blue-yellow, and light-dark. This explains why we never see "reddish green" or "bluish yellow" — these channels are mutually exclusive. Both theories are correct: trichromacy describes the receptors, opponent processing describes the neural encoding.
Color vision deficiencies
Protanopia (1% of males): absence of L (red) cones. Reds appear dark; red-green distinction is lost. Deuteranopia (1% of males): absence of M (green) cones. Similar red-green confusion but with different luminance perception. Tritanopia (very rare): absence of S (blue) cones. Blue-yellow distinction is lost. Achromatopsia (extremely rare): total absence of cone function, leaving only rod-based vision — a world in grayscale.
Genetics of color blindness
The genes for L and M cone opsins are on the X chromosome, which is why red-green color blindness affects roughly 8% of males but only 0.5% of females (who would need the mutation on both X chromosomes). The S cone gene is on chromosome 7, making tritanopia autosomal and equally rare in both sexes. The simulation uses the Brettel, Viénot, and Mollon (1997) algorithm to transform RGB values into the corresponding dichromatic perception.