paint and light are different. for light, you are adding colours in from black to make it brighter; for paint, you are adding colours from white to make it darker. thus, respectively, additive and subtractive colours.

here’s a quick and simple cheat sheet to help you out!

additive colours:

red + green = yellow

green + blue = cyan

blue + red = magenta

red + green + blue = white

subtractive colours:

cyan + magenta = blue

magenta + yellow = red

yellow + cyan = green

cyan + magenta + yellow = black