Turn green, perhaps (3)
I believe the answer is:
dye
'turn green perhaps' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dye that I've seen before include "Liquid used to change colour of clothes" , "Soluble substance for staining or colouring" , "Colouring matter" , "Staining material" , "Tint" .)