Color-related idioms and expressions are very common in English. Meanings of colors change across cultures. We will discuss some of these expressions here.
In the black
If a business is in the black, it is making money.
Like a red flag to a bull
If a statement or an action is like a red flag to a bull, it makes someone very angry. As you probably know, bulls get angry when you wave a red flag in front of them.
Catch someone red-handed
To catch someone red-handed is to catch them while they are doing something wrong or illegal.
Grey matter refers to your brain cells or intelligence. You will need to use your grey matter to solve tricky problems.
A red carpet treatment
You give somebody a red carpet treatment, when you consider them important.
In black and white
If something is in black and white, it is official or in writing or printing.
During daily conversations, we frequently use terms like green signals, green belt and white collar job. If someone gives you the green signal, they give you the permission to proceed. The term green belt refers to the farmlands surrounding a city or town. White collar jobs are office jobs.
Colors are also used to express your state of mind. When you are green with envy, you are jealous. When you look or feel blue, you look depressed or unhappy.
There are also some other color idioms.
A black sheep is the bad member of a group.
Red tape means bureaucratic delay in getting things done.
A white lie is a harmless lie.
Blue collar is a term used to refer to manual workers.