out of the blue = unexpectedly e.g. Out of the blue he asked me if I liked salad.
once in a blue moon = not very often e.g. She comes to visit once in a blue moon.
until one is blue in the face = endlessly e.g. You can shout and scream until you're blue in the face, I'm still going to the concert!
have the blues = be depressed e.g. He has the blues these days and walks around the office with a long face.
blue-eyed boy = a favourite e.g. He's always been a blue-eyed boy, getting special treatment from the staff.
blue blood = aristocratic origin e.g. They are blue blooded and have lived in that enormous castle all their lives.
to have green fingers = talented at gardening e.g. Have you seen her garden? She has green fingers and plants flowers in every corner!
green with envy = very envious e.g. They were green with envy when their neighbours bought that fancy sports car.
green light = permission to start e.g. We've been given the green light so we can start working on the project.
in the red = in debt e.g. The company is in the red. We'll have to start selling some of our assets.
red tape = annoying official regulations e.g. It took over 6 months for us to get a passport. There is so much red tape involved.
to catch someone red-handed = find someone in the act of doing something wrong e.g. The thief was caught red-handed trying to steal the car.
to see red = to become very angry e.g. When I heard the gossip, I saw red and went straight to her office.
red carpet treatment = formal and elaborate e.g. Last week, the president visited our city and received red carpet treatment.
paint the town red = celebrate e.g. When I graduated, we painted the town red and went clubbing all night.
black sheep of the family = someone who doesn't conform to the family's wishes e.g. We are all lawyers except for Rita who is the black sheep of the family and became an artist.
black list = list of unsuitable people e.g. He failed to report to the local police station and was black listed.
black market = source of illegal goods e.g. We couldn't find basic goods anywhere so we turned to the black market.
black out = lose consciousness e.g. She fainted, fell on the floor and had a complete black out.
a white lie = lie told to avoid hurting someone's feelings e.g. I don't feel guilty at all. It was a small white lie!
white as a sheet = very white e.g. When he heard the shocking news he became white as a sheet.
off colour = unwell e.g. He'll a little off colour. I think it has to do with the food poisoning.
show your true colours = reveal oneself as one really is e.g. I knew he'd finally show his true colours. He was acting all along.