Seen yesterday in Teruel, Spain.

This is my second sighting of such a creature. The first time (different city so not the same bird) I didn't get a good look, and suspected the poor pigeon had somehow been, um, artistically vandalized. But this one was clearly natural (PS: or not, see comments), with symmetric coloration merging perfectly into the iridescent breast.

Some cursory research did not turn up clues. Did its domestic ancestor mate with its budgie cagemate? Nah, that can't be right.

Anyway, it seems that polychromatic feral pigeons are a thing.

PS. More angles:

PPS: I was fooled by a pigeon, or rather by a pigeon artist! Well done to the sleuthers here.