<P> "Out of the blue" is an informal English language idiom that describes an event that occurs unexpectedly, without any warning or preparation . It is used as an adverb . The "blue" in the phrase refers to the sky, one from which a sudden thunderstorm is unexpected . </P> <P> Longer and more explicit variations include out of the clear blue sky and out of a clear blue sky . </P>

Where did the saying out of the blue come from