He doesn't allow colours (6)
I believe the answer is:
banner
'colours' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'he doesn't allow' is the wordplay.
I cannot really understand how this works, but
'he' could be 'ban' and 'ban' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for banner that I've seen before include "Flag with a slogan" , "Tree product; series of games" , "One prohibiting - flag" , "Especially good" , "Angry scientist" .)