November leaves intense, rich in colour (6)
I believe the answer is:
violet
'rich in colour' is the definition.
'november leaves intense' is the wordplay.
'november' becomes 'n' (phonetic alphabet: alpha, bravo, charlie etc.).
'leaves' indicates named letters should be taken away.
'intense' becomes 'violent' ('violent' can be similar in meaning to 'intense').
'violent' with 'n' taken out is 'VIOLET'.
(Other definitions for violet that I've seen before include "plant" , "Seldom" , "Mauve" , "Reddish blue colour" , "William's girl" .)