Grey-brown (3)
I believe the answer is:
dun
This clue is a double definition.
'grey' is the first definition.
(thesaurus)
'brown' is the second definition.
(I know that dun is a type of light brown)
(Other definitions for dun that I've seen before include "Dull brownish-grey colour" , "Brownish grey horse" , "Dingy brown" , "press for money" , "nag, for payment" .)