Blue essay about love (4)
I believe the answer is:
tory
'blue' is the definition.
(I've seen this before)
'essay about love' is the wordplay.
'essay' becomes 'try' ('try' can be a synonym of 'essay').
'about' means one lot of letters goes inside another.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'try' enclosing 'o' is 'TORY'.
(Other definitions for tory that I've seen before include "A British Conservative" , "blue" , "type on right? Yes" , "Politician; tyro (anag.)" , "Opponent of 8 Down and 14 Across, partner of 14 Down?" .)