Blue-green color (4)
I believe the answer is:
aqua
'blue-green color' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aqua that I've seen before include "Water; pale blue colour" , "shade" , "Water (L)" , "- Regia; - fortis" , "(Denoting) water (Lat)" .)