only redhead, is it wrong to say, "the one with red hair?" If I was the only white guy with a bunch of matins (or other races), is it wrong to point me out as the "white guy" rather than try to find some other less obvious way to single me out?

Is it racist to use a very visible attribute about someone as a descriptor? I don't think so. Are there racist intentions? Probably not. Just a very human effort to choose the easiest attribute by which to identify someone in that situation.

The only way I could see it as racist is if that feature is considered embarrassing or negative, like identifying someone by their "big nose" "nasty haircut" or similar. I don't see skin color that way. It's just another feature like blonde or red hair, or blue eyes, or gender.