Unhealthy-looking tree (6)
I believe the answer is:
sallow
I believe this is a double definition.
'unhealthy-looking' is the first definition.
(I've seen this in another clue)
'tree' is the second definition.
(sallow is a kind of tree)
(Other definitions for sallow that I've seen before include "(Of a complexion) pale brown or yellowish" , "Pale-looking - tree ..." , "Yellow-complexioned" , "Pasty-faced" , "Pale or yellowish colour" .)