Am I dumb, or is green not one of the primary colors
It depends on how you're coloring.
If you're using ink/pigments (crayons, paints, etc.) then the usual primary colors are the ones you're (probably) thinking of: Red, Yellow, and Blue. If you're being super picky about it, then Magenta, Yellow, and Cyan are "more" primary than those; you can get more colors out of CMY than RYB.
If you're using colored light, then the usual primary colors are Red, Green, and Blue. Light mixes differently than pigment, so, e.g., Red + Green = Yellow.
They're different because of how light works.
If you color a sheet of paper blue and shine a white light at it, then the blue pigment blocks a bunch of colors. Only blue light bounces back off of that paper paper to hit you in the eye. This is how we see, and we call the paper "blue".
The more colors you scribble on top of the blue, the more colors of white light is removed by the pigment. The more colors you add, the closer the paper gets to turning black.
As you add more colors, you get less light back. Red/yellow/blue or cyan/magenta/yellow are the primary colors for "subtractive" coloring.
Light is the opposite: the more colors you add, the closer the light gets to white. The more light you add, the more light you have. Red/green/blue are the primary colors for "additive" coloring.
... also, this chapter was a fun reveal.
last edited at Jul 11, 2021 6:01PM