"Rainbow vision" Is when a person can see many more colors that most other people can. This is because the person has a fourth color detector in their eye. These color detectors are actually called color receptors. Everyone is born with 3 color receptors, but some women go through a mutilation and end up with an extra receptor.
Who does this affect?
This mutation usually only affects women. So far, no men are known to have undergone this mutation, but that does not make it impossible.
How does this happen?
People are capible of seeing many colors because of an extra color receptor in their eyes.