Dollars are called greenbacks because that is the color of the backside of the paper money.
The color black is used often in expressions. People describe a day in which everything goes wrong as a black day.
The day of a major tragedy is remembered as a black day.
A black list is illegal now, but at one time some businesses refused to employ people who are on a black list for belonging to unpopular organizations.
In some cases, colors describe a situation. A Brownout is an expression for a reduction in electric power.
Brownouts happen when there is too much demand for electricity.
The electric system is unable to offer all the power needed in an area.
Blackouts were common during World War II. Officials would order all lights in a city turn off to make it difficult for enemy planes to find a target in the dark of night.
