Harold McKay sends this photo from his yard of a colour-challenged American robin, which I’ve heard other reports of around town this spring.
This appears to be ‘leucism’, a not-unusual condition in many bird species — a partial loss of normal pigmentation. I’ve seen robins with patchy white bits over the years, but never one with so pure white a breast.
Leucism differs from albinism (as in albino), which is a more-or-less total lack of pigmentation.
There does exist a ‘white-breasted robin’ species, but given their habitat is in the southwest of Australia, I feel confident in saying this isn’t one!