Dingy (4)
I believe the answer is:
drab
'dingy' is the definition.
(both can mean gloomy or dark)
This is all the clue.
(Other definitions for drab that I've seen before include "Dull-brown" , "Of a dull greenish-brown colour" , "Dull and monotonous" , "Colourless kind of bard" , "Shabby; a slattern (arch.)" .)