A dirty shade? (4)
I believe the answer is:
blue
I believe this clue is a double definition.
'a dirty' is the first definition.
(thesaurus)
'shade?' is the second definition.
(I have seen 'A shade' mean 'blue' so perhaps 'shade' could also mean 'blue')
(Other definitions for blue that I've seen before include "Miserable - cerulean" , "as the sky, perhaps" , "Azure" , "Conservative > depressed" , "See 7 Across" .)