Mark affixed to permit is bright red (7)
I believe the answer is:
scarlet
'bright red' is the definition.
(I've seen this before)
'mark affixed to permit' is the wordplay.
'mark' becomes 'scar' (mark left by an injury).
'affixed to' says to put letters next to each other.
'permit' becomes 'let' (synonyms).
'scar'+'let'='SCARLET'
'is' is the link.
(Other definitions for scarlet that I've seen before include "Cartels (anag.)" , "Let cars be this colour" , "bloody?" , "Vivid red" , "Murderer" .)