Not bright at all (4)
I believe the answer is:
drab
'not bright at all' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for drab that I've seen before include "Shabby; a slattern (arch.)" , "Dull and monotonous" , "Sombre" , "Rather dull" , "Dingy - shabby" .)