So I know the pictures here sucks, and won't provide much detail, but my little Cass has very weird coloration, and has since day one.
She never acts strangely (just a lot of glass surfing), she just looks odd compared to most bettas. She looks like the Wild-Type listed here:
except her head is more dusty. But it doesn't look as dusty as a betta with velvet, and she's not doing any flashing or such, she just loves her glass surfing, especially when there's air bubbles on the side of the tank.
Another thing is she has discolouration markings on her sides. Like, you know how when female bettas get breeding stripes, there's thing discoloured stripes going vertically up their sides? She has one thick one permanently on her right side, and a sort of splotch shaped one on the bottom of her left side. Is it normal for mutt bettas? 0.o;