Apart from the genetic reasons color blindness or color deficiency can have multiple reasons. You can suffer from achromatopsia after a head injury/brain lesion, so all your rods and cones are intact, but your color rendering capabilities, taking place in later stages in the brain are damaged. So you see only a gray shaded world. It’s even possible that your field of vision is gray shaded in only one half of your field of vision and the other half is fully colored.

Genetic achromatopsia leaves only your rods functional, so at first sight the effect is the same (gray shaded world). But cone vision has many other side effects, like very low resolution, high sensitivity to light etc.

Regarding the movie “Minority Report”:

Let’s say the transplant of human eyes is possible. Then most certainly the complete vision of the recipient will be scrambled beyond any possibility of recognition. The neurological pathways of two different persons are always different, so there’s no way that the recipient would just walk away from the clinic and enjoy his new eyes. The brain would have to learn all the seeing from the very beginning, making sense of the “pixel-noise” coming from the new eyes. This would be a long process, and I’m sceptical the brain being able to restore the full visual capacity, as it was before the transplantation.

Today, artificial retinal implants do work, but it’s a long learning process for the brain to make sense of the information. The learning process would be the more complicated with getting another person’s eyes. :)

–> This is significant. If this is indeed true, it means that colour blindness is just an “equipment” problem rather than a complex neurological problem. But retina and neurons (optic nerve) are still closely linked, it’s a huge challenge to alter it after the nature has built it.

This reminds me of the sci-fi movie Minority Report where the hero foils retinal scanners by switching his eyes. He might also have altered his colour vision as a bonus :D

1. The detection of wavelength ranges and the perception of color are different things. Color perception is taking place in the brain, so if a new range of signals arrives there’s a new opportunity and demand to interpret these new signals – as new colors, for example. But it’s not as simple as “red” cones make “red” colors. It’s a more complicated process that generates the signals we know as opponent colors by taking the signals of two or more cone types and sum these up or subtracting them (roughly: red+green=brightness, red+blue-green=red-green coding and red+green-blue=blue-yellow coding)

2. This question can be asked for almost everything that developed evolutionally. Genetic evidence gives that impression that something like this is the case.

3. If a woman is a carrier of a “color blindness gene” she doesn’t get color blind herself and for any potential sexual partner there’s no way to rule these women out by seeing any difference from women carrying “healthy” genes.
And if a man (in most cases) suffers from any kind of color deficiency or blindness the disadvantage does not seem to be too bad, as humans are social animals. And some color deficient individuals have certain advantages over “healthy” ones. Protanopes or Deuteranopes (I don’t remember, I guess both) can detect camouflage patterns better than normal trichromats. That has something to do with a phenomenon called observer metamerism. This occurs between all individuals, but dichromats have distinct patterns of color confusion which are obviously good for camouflage detection :). Colors that look metameric (alike) for trichromats need not look the same for dichromats. The third functioning cone type “tricks” normal observers into the perception of seeing the same color by countering the difference that dichromats are able to see in some cases.

Maybe because the female carriers of the genes have no evolutionary disadvantage.