Colourful instrument for the beginner (9)
I believe the answer is:
greenhorn
'the beginner' is the definition.
(greenhorn is a kind of beginner)
'colourful instrument' is the wordplay.
'colourful' becomes 'green' (I can't explain this - if you can you should believe this answer much more).
'instrument' becomes 'horn' (horn is a kind of instrument).
'green'+'horn'='GREENHORN'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for greenhorn that I've seen before include "Naive person (US)" , "One learning" , "Novice" , "Rookie (American)" , "Tenderfoot" .)