Given that saturated reds / greens are typically in the range of colours that can be outside a particular color-space …
… the choice of red to highlight out-of-gamut colours is (often) not very helpful.
A better choice would have been, say, yellow.
…or user configurable colour…
Highlight warnings come as complementary colours. Why not use that principle in this case too?
Indeed. Possibly a neutral grey or a checkered pattern might be more useful. Certainly, on the infamous lobster image, the red for printing and the blue for screen both become all but invisible on one lobster or the other.
this one please