Eventually I heard of the phenomenon of melanism in animals, less rare in snakes perhaps than in animals of other classes, and I was satisfied that the problem was partly solved.
"Far Away and Long Ago"
W. H. Hudson
melanism, the opposite of albinism, is rarer, and the only instance I have seen was that of a black bullfinch at Aldington; it had evidently been mobbed as a stranger by other birds of its kind, as it was injured and nearly dead when captured.
"Grain and Chaff from an English Manor"
Arthur H. Savory