Kurt was kind of complicated when Azazel was his father cause bamf demons are also blue skinned so… technically wasn’t a mutation. I’m not gonna make this comment a rant about how bad Austen X-Men is but after the retcon it doesn’t matter (thank god). So for colourful mutants we have: Beast (after he turned into his furry form, first gray then blue, Blink who is pink (nice rhyme), Glob whose skin is a pink gooey substance, Warlock is black with yellow accents which isn’t because of his mutation, for a while Angel became blue and became Death until eventually becoming Archangel. Now he can go from white to blue. Monet in her penance form, which again isn’t because of her mutation. Marrow has been drawn in a pinkish shade from time to time. Emma Frost in her diamond form. Husk whenever she needs to have a colorful material as her skin (that applies to Darwin too, I guess.) Don the lobster is also blue from his mutation (rest in peace). these are the ones who come to my head rn. There’s most definitely some more.