There are some white rios that are bred as "wild birds." I think they call them "Idaho Snows". I can't find anything online about them now though. From what I remember its a recessive coloring gene - I would guess it's a natural occurrence in this case though.
Ive seen several of them here in Utah hunting. They were all hens. One of them was the loudest most talkative hen I have ever seen. She just about ran us over when she came charging in! Nice pic!