Paint FBI agents into a hole (7)
I believe the answer is:
pigment
'paint' is the definition.
(I've seen this before)
'fbi agents into a hole' is the wordplay.
'fbi agents' becomes 'g-men' ('G-man' can be a synonym of 'fbi agent').
'into' means one lot of letters goes inside another.
'a hole' becomes 'pit' (a pit is a large hole).
'gmen' inserted into 'pit' is 'PIGMENT'.
(Other definitions for pigment that I've seen before include "Colouring material" , "Colouring substance" , "Paint" , "Colourful substance" , "Colour or dye" .)