Had he not lacked colour, he could have been great! (3)
I believe the answer is:
alf
'not lacked colour he could have been great' is the definition.
The definition suggests a singular noun which matches the answer.
'had he' is the wordplay.
I cannot really see how this works, but
'he' could be 'al' and 'al' is found within the answer.
A single letter 'f' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for alf that I've seen before include "See man" , "Great king briefly" , "Chap" , "Mr Garnett" , "Ramsey starter" .)