Additive vs. Subtractive Color
Mixing Light vs. Mixing Ink
Drag the circles so they overlap.
On the left you're stacking colored light - on the right, colored ink.
Same idea, opposite math.
LightAdditive · RGB
R
G
B
Drag the circles to mix colours
More overlapping light = brighter.
All three together makes white.
Ink / PaintSubtractive · CMY
C
M
Y
Drag the circles to mix colours
More overlapping ink = darker.
All three together makes black(-ish).