Crow, a bird, is also a bird name. A large crow usually bright black. -"Zhuangzi's Theory of Homogeneous Things".
It can also be an idiom, such as: silence; A crow's nest gives birth to a phoenix (a metaphor for a mediocre family giving birth to excellent children) is black. Such as crow green (the color of crow feathers. That is, black with purple and green; Also known as crow green note).