The trichromatic theory is a theory that believes three special cones in your eyes that are sensitive to red, blue, or green light. It is believed that in some people, one or more of the "special" cones do not work or are less sensitive to the colored waves. It is believed that this is the reason from which colorblindness stems from. For a nice, visual explanation of the theory, this Youtube http://www.youtube.com/watch?v=1-KzJ7_BuXM video sums it up quite nice.
I have seen evidence of this theory many times in my life. I have an uncle that is red-green colorblind and I have a close friend who is blue-yellow colorblind. It is odd sometimes when I am out with either one of them and I ask them to look at something and they ask me what is going on. But I wonder sometimes if it is a perception issue, because my friend told me that he used to be able to see blue and yellow (however, I have been susceptible to his lies before.)
I have also wondered if the illusions, such as this picture http://www.moillusions.com/wp-content/uploads/photos1.blogger.com/blogger/5639/2020/400/usa-flag.0.jpg, would work on people with colorblindness. Maybe if one could trick the cones/rods into seeing different colors that it would cause a reaction to the "dormant" ones and "reactivate" them. Its just something that I've been pondering for a while, and it is cool to see it pop up in my learnings. Plus, I used to make fun of my uncle for that when I was a kid. Little did I know that he was born with it. :/