Red is a hot color. American often use it to express heat. They may say they are red hot about omething unfair. When they are red hot thery are very angry about something. The small hot tasting peppers found in many Mexican foods are called red hots for their color and their fiery taste. Fast loud music is popular with many people. They may say the music is red hot, especially the kind called Dixieland jazz.
Pink is a lighter kind of red. People sometimes say they are in the pink when they are in good health. The expression was first used in America at the beginning of the txentieth century. It probably comes from the fact that many babies are born with a nice pink color that shows that they are in good health.
Blue is a cool color. The traditional blues music in the United States is the opposite of red hot music. Blues is slow, sad and soulful. Duke Elligton and his orchestra recorded a famous song - Mood Indigo - about the deep blue color, indigo. In the words of the song: "You ain't been blue till you've had that Mood Indigo." Someone who is blue is very sad.
The color green is natural for trees and grass. But it is an unnatural color for humans. A person who was a sick feeling stomach may say she feels a little green. A passenger on a boat who is feeling very sick from high waves may look very green.
Sometimes a person may be upset because he does ot have sometimes as nice as a friend has, like a fast new car. That person may say he is green with envy. Some people are green with envy because a friend has more dollars or greenbacks. Dollars are called greenbacks because that is the color of the back side 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 date of a major tragedy is remembered as a black day. A blacklist is illegal now. But at one time, some businesses refused to employ people who were on a blacklist for belonging to unpopular organizations.
In some cases, colors describe a situation. A brown out is an expression for a reduction in electric power. Brown out happen when there is too much demand for electricity. The electric system is unable to offer al the power needed in an area. Black outs were common during World War Two. Officials would order all light in a city turned off to make it difficult for enemy planes to find a target in the dark of night.
(VOA Special English Program, Words and Their Stories).