Conservative greeting opponent, a red (7)
I believe the answer is:
chianti
'a red' is the definition.
(I know that Chianti is a type of red)
'conservative greeting opponent' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'greeting' becomes 'hi' (hi is a kind of greeting).
'opponent' becomes 'anti' (someone opposed to something).
'c'+'hi'+'anti'='CHIANTI'
(Other definitions for chianti that I've seen before include "Italian offering" , "I can hit (anag) - alcoholic drink" , "Wine produced in Tuscany" , "European wine" , "I can hit for popular Italian wine" .)