Take the tour ×  Helmholtz distinguished between additive and
subtractive trichromatic color theories.  Additive theories
concern optical combinations of colored light sources and are
usually modelled on RGB while subtractive theories model pigment
mixing and are usually modelled on RYB or CMY.  What is the
physical basis of this distinction?  share|improve this question
Related: physics.stackexchange.com/q/14800/2451 –  Qmechanic Apr
16 '12 at 7:43 add comment  4 Answers  Colors are created in
your eye-brain system. Precisely, there's no "physical basis"
for the distinction you're talking about. Every colored surface,
when you see it colored, emits light in your direction. Same if
it is a piece of paper, paint, or a light bulb. The difference
is in the intensity of it.  However, when u project two lights
on a piece of paper, you superimpose them, then u simply "add"
light: there's more light, and the color that appears will be
produced by the average of the two original lights. BUT, this
optical average does