Coloring stuff (3)
I believe the answer is:
dye
'coloring stuff' 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 "Colorant" , "Colouring matter" , "Colour by dipping in liquid" , "Colouring material" , "Staining material" .)