Color mixing

There are three types of color mixing models, depending on the relative brightness of the resultant mixture: additive, subtractive, and average.

For practical additive color models, an equal superposition of all primaries results in neutral (gray or white).

For ideal subtractive color models, an equal superposition of all primaries results in a neutral (dark gray or black).

[1]: 6.1  Ideally transparent pigments transmit and absorb light, but do not reflect or scatter it and mix according to the subtractive model.

Ideally opaque pigments reflect or absorb light, but do not transmit it and mix according to the average model.

Most real paints reflect, transmit and scatter light, so mix according to a hybrid between the subtractive and average models.

[1]: 6.1  Paint color mixer is also affected by the media used as wetting, deagglomeration, and dispersing agents for the pigments.

[citation needed] For example, mixing red and yellow can result in a shade of orange, generally with a lower chroma or reduced saturation than at least one of the component colors.

A simulated example of additive color mixing in the RGB model. The primaries red, green, and blue combine pairwise to produce the additive secondaries cyan, magenta, and yellow. Combining all three primaries (center) produces white.
A simulated example of (idealized) subtractive color mixing in the CMY model. The primaries cyan, magenta and yellow combine pairwise to produce subtractive secondaries red, green, and blue. Combining all three primaries (center) absorbs all light and produces black. In practical CMY color models, the center is usually dark gray and a separate black pigment is required to produce black (CMYK model).
Red and yellow paints being mixed on a palette