What causes color blindness?

The answer

Color blindness, more accurately called color vision deficiency, most commonly results from genetic mutations affecting the photopigment proteins in cone cells of the retina. Normal human color vision relies on three types of cones: short-wavelength (blue), medium-wavelength (green), and long-wavelength (red). The genes for red and green cone photopigments are located on the X chromosome, which is why color blindness is far more common in males (about 8%) than females (about 0.5%); males have only one X chromosome, so a single defective gene causes the condition, while females need defective genes on both X chromosomes. The most common form, red-green color blindness (deuteranomaly), involves a shifted sensitivity peak of the green cone. Complete color blindness (achromatopsia), affecting all three cone types, is extremely rare at about 1 in 30,000.