One of my friend wants to know about colourful idioms. We both know what idioms are. She wants to know what is the meaning of "colourful idioms". She thinks that colourful idioms are related to the colours. The idioms which include a colour in it (green ,red ,yellow,black,blue etc....). But I really don't think it has anything to do with the "colour". I think "colourful idioms" means like "beautiful expressions". It's like we use colourful as an "adjective".

What do you think is correct. I really would like to hear the answer.