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• Dichromacy is a moderately severe color vision defect in which one of the three basic color mechanisms is absent or not functioning. It is hereditary and, in the case of Protanopia or Deuteranopia, sex-linked, affecting predominantly males.Dichromacy occurs when one of the cone pigments is missing and color is reduced to two dimensions.

·        Protanopia is a severe type of color vision deficiency caused by the complete absence of red retinal photoreceptors. It is a form of dichromatism in which red appears dark. It is hereditary, sex-linked, and present in 1% of males.

·        Deuteranopia is a color vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red–green hue discrimination. It is a form of dichromatism in which there are only two cone pigments present. It is likewise hereditary and sex-linked.

·        Tritanopia is a very rare color vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors

The colors of the rainbow as viewed by a person with no color vision deficiencies:

The colors of the rainbow as viewed by a person with protanopia:

The colors of the rainbow as viewed by a person with deuteranopia:

The colors of the rainbow as viewed by a person with tritanopia:

Illustration of normal and various colorblind visions using a US Flag