black sheep (n.) Look up black sheep at Dictionary.com
by 1822 in figurative sense of "member of some group guilty of offensive conduct and unlike the other members," supposedly because a real black sheep had wool that could not be dyed and was thus worth less. But one black sheep in a flock was considered good luck by shepherds in Sussex, Somerset, Kent, Derbyshire. Baa Baa Black Sheep nursery rhyme's first known publication is in "Tommy Thumb's Pretty Song Book" (c.1744).