Marked in two colours (7)
I believe the answer is:
piebald
'marked in two colours' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for piebald that I've seen before include "(Of horse) patched with two colours" , "Motley" , "(Of an animal) marked in two different colours" , "Two-coloured (horse)" , "Two-toned" .)