English composer not a green artist (2,5)
I believe the answer is:
el greco
'artist' is the definition.
(I've seen this before)
'english composer not a green' is the wordplay.
'english composer' becomes 'elgar' (I've seen this before).
'not' suggests deleting specific letters.
'green' becomes 'eco' (abbreviation for ecological).
'elgar' with 'a' removed is 'elgr'.
'elgr'+'eco'='EL GRECO'
(Other definitions for el greco that I've seen before include "Cretan-born Spanish painter, d. 1614" , "Domenikos Theotokopoulos" , "Spanish painter born 1541 in Crete" , "Greek born Spanish painter" , "Spanish artist born in Crete" .)