If Gochiruzeru taught us anything, it's that color shouldn't be an indicative of what a Poke's type is. For all we know, it could be just another normal type.... which wouldn't bother me all that much, but to some it might. >.>
I'd rather hope that they don't evolve, simply because I don't feel there will be any major differences aesthetically if they did. Also, if they didn't evolve, no wasted space for other pokes. >.>