Black perhaps worn by Edward as mark (7)
I believe the answer is:
cedilla
'mark' is the definition.
(I know that cedilla is a type of diacritic)
'black perhaps worn by edward' is the wordplay.
'black perhaps' becomes 'Cilla' (singer Cilla Black, 1943-2015).
'worn by' is an insertion indicator (outside letters are worn by those on the inside).
'edward' becomes 'Ed' (short for Edward).
'cilla' enclosing 'ed' is 'CEDILLA'.
'as' is the link.
(Other definitions for cedilla that I've seen before include "Mark, in foreign language" , "Sign to soften C" , "I called (anag.)" , "Mark indicating a softened consonant" , "Mark under the letter C in French" .)