Either that, or have Preview do something. It could be useful to have an approximate colour for the preview instead of the plain white which underlies some shader trees. Might let you spot a pokethrough more easily while posing. But if you look, I think it's the first Material in the file, .cr2 or whatever, which is the default. SkinTorso on Vicky, for instance. So it's not a problem that needs new program code to fix.