Colors outside a color space's gamut require mathematically negative primary values

Some physical colors cannot be reproduced as a positive mix of a given set of RGB primaries. Algebraically, matching such a color requires a negative weight for one or more primaries — equivalent to adding that primary to the target side of the equation. This is physically unrealizable with real light sources but mathematically coherent. It explains why CIE RGB color matching functions have negative lobes, and why some colors appear ‘imaginary’ in a given space. In practice, out-of-gamut colors are clipped or gamut-mapped during color management.

Examples

Matching wide-gamut pure red in a narrower RGB space algebraically requires G = −0.201: the narrower space cannot produce that saturated red without ‘removing’ green.

Assessment

A shader receives a color that, after conversion to sRGB, has a channel value below 0.0. What does this mean perceptually, and what are the two common ways to handle it?