Go green, say (3)
I believe the answer is:
dye
'go green say' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dye that I've seen before include "Colour (fabrics)" , "Liquid used to change colour of clothes" , "Staining material" , "Colouring; sounds like fade" , "Colouring matter" .)