Using idioms make you sound more advanced and there are tons of them. But today I chose only five idioms related to colours.
(I used Cambridge dictionary)
1. Out of the blue
If something happens out of the blue, it is completely unexpected.
* One day, out of the blue, she announced that she was leaving.
* My old roommate called me out of the blue.
2. Green with envy
to be very unhappy because someone has something that you want.
* Chad is heading off to Spain for the week, and I’m green with envy.
* Ireland’s economy turned the world green with envy. ~Times, Sunday Times (2009)
3. Gray area
a situation that is not clear or where the rules are not known.
* The difference between gross negligence and recklessness is a legal grey area.
* There is a large grey area where we don’t know what to say.
4. Catch someone red-handed
to discover someone while they are doing something bad or illegal.
* He was caught red-handed taking money from the till.
5. tickled pink (informal)
it means to be very pleased.
* I was tickled pink to be invited.
And here is a link for their (flashcards)
All the best 😉