Dull, colourless (4)
I believe the answer is:
drab
I believe this clue is a double definition.
'dull' is the first definition.
(similar in meaning)
'colourless' is the second definition.
(I've seen this before)
(Other definitions for drab that I've seen before include "Dull kind of bard" , "Not cheering" , "Dull sort of bard" , "Lacking brightness or colour" , "Drearily dull; slattern" .)