Always in black, which is OK for a speaker (7)
I believe the answer is:
sayable
'is ok for a speaker' is the definition.
(able to be said or spoken)
'always in black' is the wordplay.
'always' becomes 'ay' (archaic term for 'always').
'in' is an insertion indicator.
'black' becomes 'sable' (heraldic term for black).
'ay' inserted within 'sable' is 'SAYABLE'.
'which' is the link.
(Other definitions for sayable that I've seen before include "worth airing" , "Fit to be spoken" .)