The X-men X-girls are among us:

The Humans With Super Human Vision

An unknown number of women may perceive 
millions of colors invisible to the rest of us. One British scientist is trying to track them down and understand their extraordinary power of sight.

[…] Living among us are people with four cones, who might experience a range of colors invisible to the rest. It’s possible these so-called tetrachromats see a hundred million colors, with each familiar hue fracturing into a hundred more subtle shades for which there are no names, no paint swatches. And because perceiving color is a personal experience, they would have no way of knowing they see far beyond what we consider the limits of human vision.

Over the course of two decades, Newcastle University neuroscientist Gabriele Jordan and her colleagues have been searching for people endowed with this super-vision. Two years ago, Jordan finally found one. A doctor living in northern England, referred to only as cDa29 in the literature, is the first tetrachromat known to science. She is almost surely not the last.

[…]

Apparently only women have this mutation.