It may depend on the definition of red, but that doesn't sound true at all. Cadmium red, lead tetroxide, cinnabar, all in use for a hundred+ to even thousands o

It may depend on the definition of red, but that doesn't sound true at all. Cadmium red, lead tetroxide, cinnabar, all in use for a hundred+ to even thousands of years. I think where that comes from is that there isn't really an inorganic red that is all of stable, durable, non-toxic, and only then even then good looking. If I remember correctly, once Mas Subramanian sort of stumbled into "I guess I can try to make pigments with these compounds" he's tried making other colors, but sort of the big prize is in finding a good red with properties similar to YInMn.