Blue-Green Is A Color. Why Isn’t Red-Green?

We are all familiar with color mixing. There are things which we agree are to be called the color blue, things which are the color green. When these colors are put together, we would all agree that they would be somewhere in the middle.

Like these photos of a blue-green iris and computer art:

But no matter how much egg nog you have, you cannot see a color which you would describe as red-green (even if you stare cross-eyed at the Christmas tree).

Let’s shed some light on this:

The light that we can see is known as an electromagnetic wave, the same stuff that radio waves and microwaves are made of. Light travels in tiny bits called photons. The photons come from the sun, bounce off of things, and some of them make their way into our eyes. In short, when you see something, you are only really seeing it because your eyes can detect the light that gets bounced off of what you are looking at.

Wavelength in the world, color in your brain:

You have probably seen light that has been split by a prism, like this one:

A prism like this can separate the photons of light by their energy level, or wavelength. When a photon of a certain wavelength bounces into our eyes, our brain picks up the signal and you perceive the color we would all agree is red. Nothing is any color until your brain decides it is; it just reflects photons.

Blame it on the brain:

In the back of your eye, you have cells called cones, which are the main color detecting cells in your eye. When a photon hits the cones, they send a signal to your brain for processing. One of the leading theories on how your brain processes color information is called the opponent process theory.

It turns out that your eyes look at color in two channels: red vs. green and blue vs. yellow. Red and green oppose each other, and so do blue and yellow. Your eye looks at each combination of photons coming in, and calculates the amount in each channel.

The result?  Our brain first decides if something is red or green, then blue or yellow. Then it can mix the two channels. You can combine red and blue to get purple, but Lady Gaga won’t be wearing a red-green or blue-yellow headpiece at the grammys.

(eye photo credit: melloveschallah; blue-green smoke photo credit: Paralog; christmas tree photo credit: versageek; prism photo credit: hans s)