@myself Oops. "Something with an unclear rule..."

Yes. We do use 'red herring' to mean an irrelevant distraction or a false lead in an investigation.

Another common colour idiom is 'Once in a blue moon', which means extremely rarely.

Tickled pink - to be amused by something 

Green with envy - to be envious of something

Feeling blue - to feel sad 

To be yellow = To be a coward

Silver bullet, golden rule