Are We All Colorblind?

Since I'm on the subject, if you never read this old article (Looking for Madam Tetrachromat) in Red Herring (12/4/2000), it's an interesting read. In the absence of a Red Herring login, this Google search will find you a copy.

"Oh, everyone knows my color vision is different," chuckles Mrs. M, a 57-year-old English social worker. "People will think things match, but I can see they don't." What you wouldn't give to see the world through her deep blue-gray eyes, if only for five minutes.
Preliminary evidence gathered at Cambridge University in 1993 suggests that this woman is a tetrachromat, perhaps the most remarkable human mutant ever identified. Most of us have color vision based on three channels; a tetrachromat has four.

The theoretical possibility of this secret sorority -- genetics dictates that tetrachromats would all be female -- has intrigued scientists since it was broached in 1948. Now two scientists, working separately, plan to search systematically for tetrachromats to determine once and for all whether they exist and whether they see more colors than the rest of us do. The scientists are building on a raft of recent findings about the biology of color vision...