Not brightly colored (4)
I believe the answer is:
drab
'not brightly colored' 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 "Dowdy" , "Cheerless, colourless" , "Gloomy" , "Dingy, dull" , "Dull and colourless" .)