light the blue touchpaper

amber light

Hesitance to proceed; limited approval or permission to proceed.

blue chamber

A forbidden room.

blue devils

Low spirits; depression.

blue moon

A long time.

blue note

The flatted 5th scale degree in the blues scale.

blue ribbon

Highly superior in quality, style, substance, prestige, etc.

blue state

A state of the United States voting Democratic in a given election, or tending to vote Democratic in general.

blue wall of silence

Strict secretiveness maintained by the members of a police force with respect to information which might be contrary to their interests, especially information concerning questionable police actions.