I typically see more rew and black buns in the PAH adoption bit, than any other.
I have a white, a black and an agouti coloured rabbit. I'd find it hard to choose between white or black for my fav coloured bun, but colour is of no importence to me.
People that will only take on a bun of a particular colour, in my mind are unlikely to provide a loving forever home, so maybe it's as well they do get over looked until somebody worthy of such buns comes along.