Clear but unattractive (5)
I believe the answer is:
plain
I believe this is a double definition.
'clear' is the first definition.
(similar in meaning)
'unattractive' is the second definition.
(similar in meaning)
'but' is the link.
(Other definitions for plain that I've seen before include "Clear, candid" , "Unattractive - flat" , "Unadorned, not elaborate" , "Not elaborate; clear" , "Simple, ordinary" .)