Characters in highbrow hit established as brightest (7)
I believe the answer is:
whitest
'brightest' is the definition.
('white' can be similar in meaning to 'bright')
'characters in highbrow hit established' is the wordplay.
'characters in' indicates the answer is hidden within the clue.
'WHITEST' is hidden within 'highbrow hit established'.
'as' is the link.
(Other definitions for whitest that I've seen before include "Most pale" , "Having the least amount of colour" , "Superlatively clean" , "Having the least coloration" , "Cleanest" .)