'Out of the blue' is a terse form of the expression 'out of a clear blue sky' (to mean 'unexpectedly, without foreshadowing').
It is not really a figure of speech, but an idiom. ('idiom':: an established expression in a language where the meaning is not necessarily what one would anticipate from the given meaning of the individual words).
its an idiom
Simile
Onomatopoeia
Onomatopoeia
I believe this is a simile.
its an idiom
idiom
Hyperbole
simile
Onomatopoeia
The phrase "on the fence" is an example of an idiom, specifically one that is used to describe someone who is undecided or uncommitted about a particular issue or decision.
Onomatopoeia
Simile
I believe this is a simile.
i need help
Personification.
A figure of speech