Green but sensible (4)
I believe the answer is:
sage
This clue is a double definition.
'green' is the first definition.
(sage green is a kind of green)
'sensible' is the second definition.
(thesaurus)
'but' acts as a link.
(Other definitions for sage that I've seen before include "Fragrant herb having wisdom" , "Wise man - flavoursome plant" , "Seasoning for the wise one" , "cheesemongers associate with Derby" , "Oracle; herb" .)