= Additive color
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<Additive color> produces a <color> stimulus by superposing <light> from different sources. For mutually incoherent sources, their spectral <intensities> add, and the combined <optical spectrum> drives the observer's receptors. Red and green display primaries can therefore give a yellow appearance without emitting only yellow-wavelength <light>.
Project two colored beams onto the same diffuse screen and compare their overlap with the separately illuminated regions. Holding the surroundings and adaptation fixed makes the comparison interpretable. The attainable <colors> depend on the primary <optical spectra> and their allowed powers, which define a device <gamut>; merely naming three primaries does not specify every stimulus they can produce.
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