Very pale: he's an eccentric (5)
I believe the answer is:
ashen
'very pale' is the definition.
(I've seen this in another clue)
'he's an eccentric' is the wordplay.
'eccentric' is an anagram indicator.
'hes'+'an'='hesan'
'hesan' with letters rearranged gives 'ASHEN'.
(Other definitions for ashen that I've seen before include "bleached" , "Pale (faced)" , "of Tree" , "pale in colour" , "Wan - wooden - pallid" .)