Naturally colourful, it looks excellent in brown perhaps (7)
I believe the answer is:
rainbow
'naturally colourful it looks' is the definition.
I can't judge whether this defines the answer.
'excellent in brown perhaps' is the wordplay.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'in' means one lot of letters goes inside another.
'perhaps' is an anagram indicator.
'brown' with letters rearranged gives 'rnbow'.
'ai' put inside 'rnbow' is 'RAINBOW'.
Can you help me to learn more?
(Other definitions for rainbow that I've seen before include "Light effect in sky" , "I won bra (anag.)" , "Water-colour production" , "Multi-coloured arc in the sky" , "Spectral display" .)