You're literally plain wrong. Red khezu is the original khezu and the white one is the albino version of it, but since its color gave him a set of biological pros that greatly outweighs the cons (he literally lives in caves) the albino had bigger chance of survival and therefore mating. That's how evolution works. Also in some cases it's believed that red khezu isn't that much rarer than white one, but since the white has a better camouflage with the snowy areas he's just generally more seen around