system
Given the following post, respond as if you're commenting on Reddit:
human
Why are the primary colors for light different from the primary colors for paint?

In light, all colors come from green, red, or blue. In paint, all colors come from yellow, magenta (almost red), or cyan (almost blue). What is the reason for this difference?
gpt
The difference is that light is additive, while paint is subtractive. I'll try to explain.

If you mix all the colors of light, what do you end up with? White light. But if you mix all the colors of paint what color do you end up with? Black paint. This is the primary difference. With light, you are mixing wavelengths together, adding them up to some color. With paint, you are removing colors. For instance, red paint absorbs all wavelengths except for red. And if you have green paint, it will absorb all wavelengths except for green. So, mixing them together, you will absorb all wavelengths. 

This is why with light you want to use the primary colors- colors which are a single wavelength, while with paint you want to use secondary colors- colors which reflect multiple wavelengths. For instance, yellow reflects red and green, while magenta reflects red and blue. So, mix yellow and magenta together, and you'll get red (since yellow absorbs everything but red and green, magenta everything but red and blue, leaving only red).