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True color blindness (the lack of color sensation) is rare. It can be found in rod monochromats (people with only rods) and/or as a result of some brain injuries (color-sensitive blobs are most sensitive to oxygen deprivation). Color deficiency, however, is more common, and results from the lack of one of the cone pigments. The three different types of color deficiency include:

Protanopia: There is no L (long wavelength, or red) pigment. This makes it hard to distinguish between red and green, making reds look particularly dark. This affects a few percent of the male population and a very small fraction of a percent of the female population (since the genes for the cone pigments are located on the X chromosome).

Deuteranopia: There is no M (medium wavelength, or green) pigment. This makes it hard to distinguish between red and green. It affects a few percent of the male population and a tiny fraction of a percent of the female population.

Tritanopia: There is no S (short wavelength) pigment. This makes it difficult to distinguish yellows, greens, and blues. This kind of color deficiency is very rare.

Watch this video to learn more about colorblindness!