Leucistic Bird Hanging Around

A couple of posts ago I asked for opinions on a bird coming to my backyard feeder here in Minnesota. The majority of opinions were that I was being visited by an aberrant House Finch.

Well it's still around and I got a better look at it.

Even though the photo was taken through a window screen this is about as well as I have seen it. The primaries and wing coverts are actually lighter than the rest of the bird. The eye is dark. I still think this a House Finch, though a couple of people suggested an escaped canary.

So the question today is not about species (unless someone has a better ID), the question is about the mechanism of the strange feather color. I assume something genetic but not albinism. Whatever the cause it seems the bird is in good health, has been present for a while and doesn't seem to mind the snow.

Pretty fun having this bird around. Now if I could just coax that Lewis' Woodpecker in Wisconsin over to my suet feeder...