Kind of grey sock dipped in Merlot, say (8)
I believe the answer is:
graphite
'kind of grey' is the definition.
(colour)
'sock dipped in merlot say' is the wordplay.
'sock' becomes 'hit' (I've seen this before).
'dipped in' is an insertion indicator.
'merlot say' becomes 'grape' (type of grape).
'hit' going within 'grape' is 'GRAPHITE'.
(Other definitions for graphite that I've seen before include "Form of carbon used in pencils" , "Black carbon used in lead pencils" , "mineral" , "Pencil-lead carbon" , "black stuff" .)