Gamut Warning
A soft-proofing overlay that flags pixels whose colours the destination profile cannot reproduce.
In depth
The warning shows where colours will be substituted, which matters less for isolated pixels than for large areas — a broad out-of-gamut region will lose its internal gradation and print as a flat patch. The remedy is to reduce saturation or adjust the hue slightly in that range until the flagged area shrinks.
Examples in practice
A gamut warning across a whole field of poppies signals that their petal detail will flatten unless saturation is eased.