Fruit black? Exactly! (5)
I believe the answer is:
plumb
'exactly' is the definition.
(plumb can mean exactly or precisely)
'fruit black?' is the wordplay.
'fruit' becomes 'plum' (plum is a kind of fruit).
'black?' becomes 'b' (as in pencil classifications).
'plum'+'b'='PLUMB'
(Other definitions for plumb that I've seen before include "Lead weight for measuring depth" , "Weight to show vertical direction" , "Exactly - perpendicular" , "Reach or experience, say the depths" , "Connect pipes" .)