Coming down U.S. 30 south out of Kemmerer, Wyoming Saturday morning, about ten miles north of I-80 I saw a road-kill pronghorn that was very dark, almost black, on the upper part, normal white below. Driving cross-country for 15+ years I've seen a lot of pronghorns but never much variation in color.

Is dark/black as unusual as my experience would indicate or are there several of them but just road-shy??

I saw one 2 years ago, alive. I also have seen 2 white ones. I saw a black mulie fawn and have PICS of an albino mulie buck.

Yes the color variation is very rare.
I have no scientific numbers to quote you but I can say that I have been a full on hunter, hiker and outdoorsman always looking at animals of all types for 35 years and have never seen a deer, elk or antelope with a color variation that was substantially deviated from the norm. My brother has seen 1 mule deer that had a white "paint" mark on it.
Elkman count yourself lucky to see all those.

I had a white albino Mule deer buck on our ranch, but a neighbor finally shot it..I was upset over that but he had every right to do so. I never said a word about it to him.. Apparantly none of his off spring was white, at least not while I was there but I understand that albino gene can lay dormint for years, then spring up out of nowhere. I had a neighbor that said he had two paint deer on his place.

About 5 years ago in the So. Hills (Unit 54) behind Twin Falls, Id. my son and I and a friend of his sat on a rock ledge and watched two half grown Lion cubs playing and mauling their mother. Both cubs were pure white with pink eyes. They were about 75 yards from us, the mother saw us and jumped in the Shiney brush but the cubs just sat and starred at us and went back to their antics..We watched them for about another 30 minutes and then they walked of into the brush and disapeared...To this day I have not heard of another sighting of them nor or either one being killed or found dead??????????

That made my hunt for that year..I wouldn't take for that experience..