Color-Math

What is the difference between adding and subtracting colors? What does that even mean?

Sometime around kindergarten, we learn that there are three primary colors – red, yellow, and blue – and that mixing red and yellow paint makes orange paint, red and blue makes purple, and yellow and blue makes green. Sometime later – sixth grade science, perhaps – we learn that light has different primary colors: red, blue, and green. But color is made of light, right? How can these two rules be reconciled?

There is a difference in primary colors and their resulting mixtures because of what the forms of color do. Paint is a material that changes the hue of color that is reflected from the paper. For example, white paper reflects all colors; putting yellow paint on the paper means that only yellow light is reflected. When the yellow is washed over with blue, the only light that is reflected is the light in the color spectrum that borders on both yellow and blue: green is left. And when green is washed over with red, only brown or black is reflected. This narrowing, decreasing range of color hues reflected from the painting – starting at white and progressing to black – is an example of subtractive color mixture.

Imagine the opposite scenario. You start with a dark space; no light shines into it. It is black. Next, a green light is switched on. The space is lit with a green hue. Then a red light is turned on. The space becomes yellow: more wavelengths of light are available. Finally, a blue light is turned on. The space is filled with white light, because it contains all of the wavelengths of light visible to the human eye. This process of light addition – starting at black and progressing to white – is an example of additive color mixture.

Therefore, in subtractive color mixture, more and more light is absorbed when colors are mixed. In additive color mixture, more and more light is reflected or produced when colors are mixed.