Americans have used colours to create many expressions they use every day. We say we're "in the pink" when we are in good health. It is easy to understand how this expression was born. When my face has a nice fresh, pink colour, it is a sign which shows my health is good. The colour green is natural for trees, it is an unnatural colour for humans. When someone doesn't feel well, for example, we say he looks green. When someone is angry because he doesn't have what someone else has, we say he is "green with envy". Some people are "green with envy" because someone else has more dollars, or "greenbacks". Dollars are called "greenback" because that's the colour of the backside of the money. Blue is a cool colour. The traditional blue music of American blacks is the opposite of red hot music. It is slow, sad and soulful  . To be blue, of course, is to be sad. The colour black is often used in expressions. People describe a day in which everything goes wrong as a "black day". A "black sheep" is the member of a family or group who always seems to be in trouble. If someone meets a "black cat", something unlucky might happen to him. Not all the "black" expressions have bad meanings. A company "in the red" is losing  money. If someone tells you to put someone "in black and white", they want you to write it down. My brother is   _   of our family, everyone hates him.
a black horse a black cat a black dog a black sheep