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Higher brain areas implicated in color processing include the parvocellular pathway of the lateral geniculate nucleus of the thalamus, and visual area V4 of the visual cortex.
Acquired color blindness is generally unlike the more typical genetic disorders.
Transient color blindness also occurs (very rarely) in the aura of some migraine sufferers.
The different kinds of inherited color blindness result from partial or complete loss of function of one or more of the different cone systems.
The sensitivity of normal color vision actually depends on the overlap between the absorption spectra of the three systems: different colors are recognized when the different types of cone are stimulated to different extents.
For example, red light stimulates the long wavelength cones much more than either of the others, but the gradual change in hue seen, as wavelength reduces, is the result of the other two cone systems being increasingly stimulated as well. The most common are red-green hereditary (genetic) photoreceptor disorders, but it is also possible to acquire color blindness through damage to the retina, optic nerve, or higher brain areas.
Some may not even be aware that their color perception is in any way different from normal.They are collectively referred to as "red-green color blindness", though the term is an over-simplification and somewhat misleading. They include problems in discriminating blues from yellows, and the rarest forms of all, complete color blindness or monochromacy, where one cannot distinguish any color from grey, as in a black-and-white movie or photograph.Congenital color vision deficiencies are subdivided based on the number of primary hues needed to match a given sample in the visible spectrum.Normally, there are three kinds of cones, each containing a different pigment.The cones are activated when the pigments absorb light.