Comment by dentemple

Like the other person said, most forms of colorblindness is caused by genetics--specifically, recessive traits. So, it's the sort of trait that will run in the family.

To help explain our experience, it's like trying to distinguish between two similar shades of yellow. It'll be clear and obvious that both are the color yellow. When there's only one example of each standing next to each other, it'll be easy to tell which shade is the lighter one, even if it's only slightly different. But if you had a sea of examples and are asked to pick out which yellows are slightly lighter than the other ones, then it might cause you to stop and study them for awhile to figure it out.

It's just like that for the common forms of colorblindness (where the color cones in the eyes are bent, but not missing), but instead of this metaphorical "yellow" it's this special "red-and-green" color that we see that's different from what everyone else sees. It's like trying to distinguish between two different shades of the same color, where it's obvious which is which when there's only two examples to compare to but not so much when your entire field of vision has bits of one hidden amongst a sea of the other. It's like red and green are a spectrum of the same color rather than being two separate ones.