Okay, you saw that I reported Okay, what bird is this? and Update: it's probably a Brewer's Blackbird with pigment mutation.
From the first of these, we have reports from John and Robin of photo by Robinsegg:
Tough break for this guy. Brewer's Blackbirds are very social birds. They gather in great numbers in the city park(typical) where this shot. Unfortunately, the rest of the flock wouldn't have anything to do with him.
The one I spotted seemed to be fitting in better, but speaking as a nerd …
UPDATE from John:
Leucism is an abnormal reduction in pigmentation (color). It's like albinism,only not as complete. I've seen some blackbirds and crows that exhibit it, though that bird you photographed was a really dramatic example.
[The other] photo was uploaded on September 19 of this year, and without knowing
where it was taken, I could almost believe that's the same bird you photographed. The pattern of white feathers is a little different, but I could see that being the result of the bird's having molted some between the two pictures. But I suppose it's more likely that it's just a case of leucistic blackbirds tending to have white pigmentation in similar locations on their bodies.