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Quick Questions cracks the code of color vision, color blindness, and even newly discovered sort of technicolor vision!
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Sources:
http://www.simoneye.com/blog/how-many-colors-do-we-actually-see

http://discovermagazine.com/2012/jul-aug/06-humans-with-super-human-vision

http://www.colourblindawareness.org/colour-blindness/

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001997/

http://genetics.thetech.org/ask/ask349

http://academic.evergreen.edu/curricular/anp07/Looking%20for%20Madam%20Tetrachromat.htm

http://micro.magnet.fsu.edu/primer/lightandcolor/humanvisionintro.html
You might tend to assume that everyone sees the world in pretty much the same way, within the same sets of colors that we call visible light, as if we were all coloring with the same box of crayons.

But the truth is, how many colors you can perceive actually depends on what you're working with.

Our eyes are these amazing energy converters, taking light energy and turning it into chemical energy and transmitting it to our brains through nerves. And within our retinas at the backs of our eyes are receptor cells called cones and rods.

Rods allow us to see in black and white and grey, and they're still effective in dim light, and most humans have more than one hundred and twenty million of them. Cones on the other hand are they eye's color receptors, we only have six million of those, and they enable us to see fine detail in well-lit conditions.

Most people have three types of cones: blue, red and green, and each receptor is triggered by different wavelengths of light. The brain combines the signals from the three types of receptors to produce what we perceive as color.  When you put all the various combinations from these three receptors together, most humans can see about one million colors. This is called trichromacy.

Color-blindness usually occurs when a person is missing one of those cone receptors - almost always either red or green. This is called dichromacy, and it reduces the ability to distinguish between those two colors.

Interestingly, there are varying degrees of color blindness. Dichromatics can see about ten thousand colors, but humans with monochromacy, who are missing two or all three types of cones, only perceive about one hundred colors - mostly shades of grey.

And because the genes that affect color vision are on the X chromosome, disparities in color vision often correspond with your sex.

Biological males only have one X chromosome, so they're more likely to inherit color blindness - about 8% of men have some form of it. But biological females have two X chromosomes, so for them to be affected they have to have the color blindness trait on both of their sex chromosomes. As a result, color blindness in women is really rare, showing up less than 1% of the time.

But the X chromosome is also where scientists have recently found a genetic mutation that may be linked to a sort of technicolor superpower.

In 2010, British scientists identified the first known Tetrachromat - a woman whose eyes has a fourth type of cone that can register shades between red and green - basically enabling her to perceive at least one hundred million colors.

This, too, seems to be a sex-linked trait, and other studies have suggested that as many 3% of the world's women may have this ability, in which case paint companies and crayon makers are gonna have a lot of new names to come up with.

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