What is the origin of the idiom "black sheep" and when to use it?

The idiom "black sheep" originated in the early 18th century. It refers to the world of sheep farming, where black sheep were considered less desirable because their dark wool could not be easily dyed or blended with white wool. This association led to the metaphorical use of "black sheep" to describe a person who stands out or deviates from the expected norms within a family or group. The idiom is typically used in a negative way to describe someone who is different from the others in a family or group.