Color of an overcast sky (4)
I believe the answer is:
gray
'color of an overcast sky' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gray that I've seen before include "An Anatomist; an Elegist" , "(Churchyard) Elegy poet" , "dull for Americans" , "Elegiac poet" , "In America, dull" .)