Do Remarkable Female Mutants Walk Among Us? . “Most people are trichromats, with retinas having three kinds of color sensors, called cone photopigments — those for red, green, and blue. The 8 percent of men who are color-blind typically have the cone photopigment for blue but are either missing one of the other colors, or the men have them, in effect, for two cone photopigment, for a color between red and green.

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.

Besides the philosophical interest in learning something new about perception, the brain, and the evolution of our species, finding a tetrachromat would also offer a practical reward. It would prove that the human nervous system can adapt to new capabilities. Flexibility matters greatly in a number of scenarios envisaged for gene therapy. For example, if someone with four kinds of color photopigments cannot see more colors than others, it would imply that the human nervous system cannot easily take advantage of genetic interventions.

For years now, scientists have known that some fraction of women have four different cone photopigments in their retinas. The question still remains, however, whether any of these females have the neural circuitry that enables them to enjoy a different — surely richer — visual experience than the common run of humanity sees. “If we could identify these tetrachromats, it would speak directly to the ability of the brain to organize itself to take advantage of novel stimuli,” says Dr. Neitz. “It would make us a lot more optimistic about doing a gene therapy for color blindness.”

Red Herring