Dismal shade (4)
I believe the answer is:
blue
I believe this clue is a double definition.
'dismal' is the first definition.
(I know that dismal can be written as blue)
'shade' is the second definition.
(I know that blue is a primary color)
(Other definitions for blue that I've seen before include "Unhappy a sportsman at university" , "Sunny sky or low spirits" , "Tory?" , "in Oxford, it's dark" , "Sad, melancholy" .)