More on 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, because the genes for the red and green color receptors are located on the X chromosome, of which men have only one and women have two. Such a trait is called sex-linked.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Protanopia (1% of 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. They have a neutral point at a wavelength of 492 nm?that is, they cannot discriminate light of this wavelength from white. For the protanope, the brightness of red, orange, and yellow is much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows and from greens primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed as to be invisible. E.g. Pink flowers, reflecting both red light and blue light, may appear just blue to the protanope.
(Wikipedia link below also has color tests. See if you're
color blind, if you want.)
What no ones sees:
Bird colour vision differs from that of humans in two main ways. First, birds can see ultraviolet light.