Prefix Un- and Re-

The prefix 'un-' means 'not' or 'the opposite of'. For example, 'happy' becomes 'unhappy', which means 'not happy'.

The prefix 're-' means 'again' or 'back'. For example, 'play' becomes 'replay', which means 'to play again'.

No, 'unblue' is not a real word.

The opposite of 'happy' is 'unhappy'.

'Rewrite' means to write something again.

'Replay' means to play something again.

'Unfix' means to take something that was fixed and make it not fixed.

Yes, you can use 'un-' to make a word mean the opposite. For example, 'do' becomes 'undo', which means 'to reverse the action of doing'.

An example of a word with the prefix 're-' is 'rewrite'.

'Unhappy' means not happy.