Claret's possibly this shade of red (7)
I believe the answer is:
scarlet
'this shade of red' is the definition.
(I've seen this before)
'claret's possibly' is the wordplay.
'possibly' is an anagram indicator.
'clarets' with letters rearranged gives 'SCARLET'.
(Other definitions for scarlet that I've seen before include "Cartels (anag.)" , "Cherry-red" , "Crimson" , "bloody?" , "immoral" .)