Tetrachromacy:

Normal human vision is a combination of three different photoreceptors that are sensitive to red, green, and blue. The genes for the red and green photoreceptors are located on the female sex chromosome, X, while the blue lies on a separate chromosome. Now, in a rare genetic occurrence, it may happen that an X chromosome obtains two 'different' red photoreceptors or two 'different' green photoreceptors, instead of the a red and a green. These 'different' receptors would respond to slightly different wavelengths of light. For example, if an X chromosome had two different green photoreceptors, one would respond to one shade of green and the other would respond to an alternate shade of green.

Now say a female carrier of this mutated X chromosome has a female child (a female would have two X chromosomes as opposed to the XY of a male. The Y chromosome generally contains no genetic material.) Then, this female child would have an X chromosome with genes for two slightly different photoreceptors responding to the same color, and an X chromosome that is perfectly normal (with both a red and a green photoreceptor gene). Thus, this child would be tetrachromat- they could essentially be capable of seeing an extra color, somewhere in between red and green.

(This is funny because my friends and I as kids always used to think up names for new colors. The best name we came up with was 'GLOW,' which was the color of the setting sun reflecting off our friend’s parents’ Buick.)

Now, it is uncertain whether the brain can process this fourth photoreceptor to make sense out of the extra color, but given the plasticity of the brain, it is likely.


Here's a quote I found about the possible 'application' of tetrachromats:

"But this could be a good thing [tetrachromacy], making tetrachromats invaluable for jobs involving color comparison, such as authenticating artwork and pattern matching, or for recognizing subtle distinctions in skin tones for patient diagnosis, mood reading, lie detection, and make-up artistry. In addition to seeing more colours [yeah, it's British], a tetrachromat might possess a red photopigment shifted slightly further into infrared wavelengths, enabling them to see beyond the natural limit of human perception, allowing for cat-like night-vision, and perhaps even directly perceiving hints of body heat." (Ryan Sutherland in "Aliens among us: preliminary evidence of superhuman tetrachromats.")

(That last sentence seems a little sensational. THE PREDATOR DOES EXIST AND HE CAN SEE YOUR BODY HEAT! OH SHIT! WE'RE SO FUCKED!)