Most people think crows are black , and most are.
A number of species in the genus Corvus , however, have extensive white in their plumage. Some other species have extensive white on other parts of their bodies as well. Even those species that normally are black may show patches of white on parts of their body, or may be completely white. American Crows, Corvus brachyrhynchos , frequently show problems with pigment deposition. I find young like this every year, and the occurrence is about what I would predict based on seeing abnormal crows in large foraging flocks.