A color space's gamut is the subset of all human-visible colors it can reproduce

Not all physical colors can be reproduced by any given RGB color space. The gamut is the set of colors reachable as non-negative combinations of the space’s primaries. On the CIE chromaticity diagram the gamut appears as a triangle; colors inside are representable, colors outside are not. Wider gamuts (Display P3, Rec. 2020) reproduce more saturated colors than sRGB. When a color falls outside the target gamut, it must be clipped to the nearest in-gamut color or compressed via a gamut-mapping algorithm.

Examples

A vivid cyan in RAW photography may fall outside sRGB but inside Display P3. Rendering to sRGB without gamut mapping clips the blue-green, making it appear duller.

Assessment

An image captured in a wide-gamut RAW format is displayed on an sRGB monitor without conversion. The bright greens look grayish. Why, and what is the fix?