Ok, I’ve been working on this blog for a while now, and it’s supposed to be about photography and perception from a colorblind perspective . . . and I haven’t mentioned a thing about colorblindness yet. So let’s remedy this little problem. Whenever someone finds out that I’m colorblind, the first question I always get (ALWAYS) is, “so . . . what color is my shirt?” And if you were tempted to ask, you, like most of the population, do not understand colorblindness.

I suppose I should mention that there are multiple types of colorblindness, and that I am red-green colorblind. That’s the common type (affecting something like 10% of all males, believe it or not) and in my case is known scientifically as protanomaly (there is another type of red-green colorblindness, deuteranomaly which makes up a portion of that 10%, but they are often difficult to distinguish).

Ok, so what is colorblindness? Well people have 4 types of light receptors in their eyes: 1 type of rod, and 3 types of cones. Rods are proteins that are sensitive to a broad spectrum of light (ie all colors) – whenever light reaches a rod, it sends a signal. That means that rods can’t discriminate between colors, just intensity of light. Rods are active in low light because they’re really sensitive. Your ability to discriminate colors in the dark would be similar to what a monochromat sees normally (monochromats don’t see any color, but this is less than 1% of cases of colorblindness).

Cones, on the other hand, are sensitive to a particular portion of the light spectrum. Generically we would say that there are red cones, blue cones, and green cones . . . though that’s not entirely acurate, it’s close enough. This is why TVs, computer monitors, cameras, all sorts of image capturing and reproducing devices use RGB color – because those are the same color primaries that your eye sees. Whether you believe it or not though, EVERYONE is colorblind to certain colors. There are way more colors in the spectrum than what you can reproduce using only red, green, and blue primaries. But since humans can’t distinguish the colors, there is no need for a computer monitor to reproduce them either.

Anyway, back to being colorblind. Colorblindness is (usually) a genetic condition, and it is sex-linked (the DNA that codes for your cones is located on the X chromosome). Because males only have one X chromosome (males are “XY”), they only have one copy of the code for cones . . . if that one copy is defective, you’re colorblind. Females have two X chromosomes (females are “XX”), so unless both copies are defective, you’re color normal. By the way, there is good evolutionary reason for males to be prone to colorblindness and females to be color normal – females traditionally gathered food and needed to know the difference between a red berry and a green one, while males who were hunting benefitted from being colorblind because they can see through color-based camoflauges.

So most colorblind individuals have a “deformed” version of one of their cones (usually either the red cone or the green cone, with red cone deformations being more common). Now, the spectrum for all the cones overlap slightly, but a deformation causes the spectrum of that cone to shift closer to to one of the other cones. For example, a deformed red cone is a bit more sensitive to greens than it should be, and a little less sensitive to reds than it should be. As a result, reds don’t look as saturated or bright as they should, and some green colors can actually look red.

The part that confuses most people is that a bright saturated red still looks red to a colorblind person because there is SO MUCH red that the colorblind red cone picks up enough of it to send a signal. A very washed out red or a very dark desaturated red doesn’t have much red energy in it and thus can be missed by the defective red cone. By the same token, bright saturated greens give a strong signal to the green cone, and even if they set off the defective red cone a little the signal is swamped by the signal from the green cone . . . the colorblind brain still interpruts the color as green. Funky brownish greens or washed out greens though produce a low signal from both the normal green cone and the deformed red cone, which results in a confused signal reaching the brain.

Net, there are certain sets of colors that are easy for a normal-color person to distinguish, but look the same to a colorblind person. And when these colors are set next to eachother, the normal-color person detects a nicely contrasting image while the colorblind person sees only “noise”.