AskUs: Why do computers use red, green, and blue to create a color when the primary colors are red, blue, and yellow?

So one of our readers asked us this question the other day: Why do computers use red, green, and blue to create a color when the primary colors are red, blue, and yellow?

ANSWER

What color we see is based on what frequencies of light hit our eyes. The different frequencies are represented by the colors of the rainbow. White is what we see when we see a combination of all frequencies and black/dark is what we see when there are no photons (no light at any frequency). So what causes light to hit your eyes? Well, some things emit light such as light bulbs, the sun, your computer screen. But we also have light that hits our eyes after it bounces off an object. So that blue car on the street? It’s not emitting a blue light, but white sunlight is hitting that car, and blue light is bouncing off of it into our eyes.

Why did the white light change to blue light when it bounced off a blue object? Because light can be absorbed, and all of the frequencies in the white light (which remember, white is a combination of everything in the rainbow) got absorbed except blue.

So there are two ways to create colors: emitting frequencies you want and absorbing the frequencies you don’t want. If you start with nothing (black/darkness), you can create any color you want by adding together red, green, blue light frequencies (additive). If you start with everything (white) you can get any color you want by subtracting/absorbing red, yellow, blue (subtractive).

So the primary colors for subtracting light are red, yellow, blue and we use those when painting. And the primary colors for adding light are red, green, blue and we use those for computer screens and TVs. I think technically the specific shades you need to get every other color out of subtractive lighting are magenta instead of red and cyan instead of blue (and yellow is still yellow).

In short, computers and TVs are about emitting the colors we want. Paintings are about absorbing the colors we don’t want from the white light around us in order to get the colors that we want