It depends on how you use it. If you mean literal colors, then it's not an idiom. If you say something like "It's all there in black and white," then it's an idiom meaning that something is printed.
Just a flowery word for day.
It means to be very angry.
There aren't any idioms that mean "black" that I know of. There are plenty of similes, like "black as the ace of spades."
This is not an idiom. It is comparing one thing to another, so it is a simile. Remember: "AS ___ AS___" means A Simile! It is just saying that something is very black.
It's not an idiom. It means just what it says -- it's either going to rain that day, or it will be sunny.
In debt. Its antithesis, "in the black," refers to having a balanced budget.
It takes a long time to do an important job
It refers to a day being noteworthy or of hanging a banner of announcement, usually of good news.
The phrase means to be nervous or anxious about something.
It's not really an idiom. It means "what are you thinking about."
It is not an idiom, it means your nose is itching.