Wizard backed green hair (7)
I believe the answer is:
warlock
'wizard' is the definition.
(I know that wizard can be written as warlock)
'backed green hair' is the wordplay.
'backed' shows that the letters should be reversed in order.
'green' becomes 'raw' (both can mean naive or inexperienced).
'hair' becomes 'lock' (a lock of hair).
'raw' in reverse letter order is 'war'.
'war'+'lock'='WARLOCK'
(Other definitions for warlock that I've seen before include "Magician; Peter ---, composer" , "Male magician - British composer, 1894-1930 - low rack (anag)" , "Charmer" , "Sorcerer" , "Wizard, magician" .)