Blue-green shade (4)
I believe the answer is:
teal
I believe this is a double definition.
'blue' is the first definition.
(I know that teal is a type of blue)
'green shade' is the second definition.
(I've seen this in another clue)
(Other definitions for teal that I've seen before include "Duck - dark greenish-blue" , "Variety of duck" , "Duck; greenish-blue colour" , "Dark green-blue; duck" , "Dark greenish-blue colour" .)