Paint, ink, crayon and dye all color things the same way: they absorb (subtract) some colors of light and reflect the rest. That is why mixing them is called subtractive mixing.
Key idea
Each pigment you add absorbs more light. A mixture reflects only what all its pigments reflect, so mixtures move toward darker and duller.
Why it works
Yellow paint reflects yellow light and some of its neighbors, green and orange, and absorbs blue. Blue paint reflects blue and some green, and absorbs most red and yellow. Mix them and each one absorbs what the other reflects, except the green that both reflect. So the mixture looks green, and a little darker than either paint.
Worked example: Why blue and yellow make green
Explain, with absorbing and reflecting, why blue and yellow paint make green.
- Yellow absorbs blue light; blue absorbs red and yellow light.
- The only light both of them reflect is green.
- So green is what reaches your eye from the mixture.
Answer: Green is the light both paints reflect.
Printing inks are subtractive too. Their primaries are cyan, magenta and yellow. Overlap them and the mixtures get darker:
| Inks | Make |
|---|---|
| cyan + magenta | blue |
| magenta + yellow | red |
| cyan + yellow | green |
| all three | a very dark, muddy brown (so printers add black ink) |
Common mistake
Expecting a mixture to be brighter than its paints. Every pigment you add absorbs more light. To keep mixtures bright, mix as few paints as you can, and mix neighbors on the wheel. To lighten, add white, which reflects all light.
The red-yellow-blue wheel is a teaching model. Real results depend on the exact pigments: a magenta-leaning red and a cyan-leaning blue mix a cleaner violet than a fire-engine red and a navy blue do.