Horse color pattern (4)
I believe the answer is:
roan
'horse color pattern' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for roan that I've seen before include "Horse with a coat of mixed colour" , "Horse with main colour interspersed with hairs of another" , "Two-colour horse" , "Reddish-coloured horse" , "Nora (anag) - horse" .)