Dull, overcast (4)
I believe the answer is:
grey
I believe this is a double definition.
'dull' is the first definition.
(I've seen this before)
'overcast' is the second definition.
(thesaurus)
(Other definitions for grey that I've seen before include "Unclear (area); dull (weather)" , "Ashen" , "Mix of black and white" , "15 [JANE] the short-lived queen" , "Colour of lead" .)