Color blindness is not the swapping of colors in the observer's eyes. Grass is never red, and stop signs are never green. The color impaired do not learn to call red "green" and vice versa. However, dichromats often confuse red and green items.
Color blindness is rare in girls.
The genes for color vision are on the X chromosome, and because females have 2 X chromosomes, if one is deficient, the other makes up for it. There are only about 1 in 200+ girls who have color deficiencies. However color blindness ranges from 5-8 % in males.
Everyone is colorblind at birth and a color defective male always inherits his deficiency from his mother, the mother however is not color blind.
Bulls are actually color blind, it is the motion of a waving red rag which angers them, not the color itself.
Total color blindness
Achromatopsia is strictly defined as the inability to see color. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to congenital color vision disorders (i.e. more frequently rod monochromacy and less frequently cone monochromacy).
Blue-yellow color blindness
Those with tritanopia and tritanomaly have difficulty with discriminating blue and yellow hues. Color blindness involving the inactivation of the short-wavelength sensitive cone system (whose absorption spectrum peaks in the bluish-violet) is called tritanopia or, loosely, blue-yellow color blindness.
Red-green color blindness
Those with protanopia, deuteranopia, protanomaly, and deuteranomaly have difficulty with discriminating red and green hues. Genetic red-green color blindness affects men much more often than women.
Monochromacy is the condition of possessing only a single channel for conveying information about color. Monochromats possess a complete inability to distinguish any colors and perceive only variations in brightness. Monochromacy occurs in two primary forms:
Rod monochromacy - Frequently called achromatopsia, where the retina contains no cone cells, so that in addition to the absence of color discrimination, vision in lights of normal intensity is difficult
Cone monochromacy - Condition of having both rods and cones, but only a single kind of cone. A cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues.
Protanopes, deuteranopes, and tritanopes are dichromats, that is, they can match any color they see with some mixture of just two spectral lights (whereas normally humans are trichromats and require three lights). Protanopes and deuteranopes see no perceptible difference between red, orange, yellow, and green.
Tritanopia (Males and Females) - Lacking the short-wavelength cones, those affected are unable to distinguish between the colors in the blue-yellow section of the spectrum. This form of color blindness is not sex-linked.
Deuteranopia (Males) - Lacking the medium-wavelength cones, those affected are again unable to distinguish between colors in the green-yellow-red section of the spectrum. This is one of the rarer forms of colorblindness making up about 1% of the male population, also known as Daltonism
Protanopia (Males) - Lacking the long-wavelength sensitive retinal cones, those with this condition are unable to distinguish between colors in the green-yellow-red section of the spectrum. This is a rare form of color blindness.
Those with protanomaly, deuteranomaly, or tritanomaly are trichromats, but the color matches they make differ from the normal. They are called anomalous trichromats. In order to match a given spectral yellow light, protanomalous observers need more red light in a red/green mixture than a normal observer, and deuteranomalous observers need more green.
Deuteranomaly - Having a mutated form of the medium-wavelength (green) pigment. The medium-wavelength pigment is shifted towards the red end of the spectrum resulting in a reduction in sensitivity to the green area of the spectrum. Unlike protanomaly the intensity of colors is unchanged.
Protanomaly - Having a mutated form of the long-wavelength (red) pigment, whose peak sensitivity is at a shorter wavelength than in the normal retina, protanomalous individuals are less sensitive to red light than normal. This means that they are less able to discriminate colors, and they do not see mixed lights as having the same colors as normal observers.
Tritanomaly - Having a mutated form of the short-wavelength (blue) pigment. The short-wavelength pigment is shifted towards the green area of the spectrum. This is the rarest form of anomalous trichromacy color blindness. Unlike the other anomalous trichromasy color deficiencies, the mutation for this color blindness is carried on chromosome 7.
Website Design for Colorblind
Good graphic design avoids using color coding or color contrasts. If you're using colors to make distinctions, you should be aware that red and green can be hard for a color blind person to tell apart. See Color Blind Spectrum Chart.