Comment about blemish (6)
I believe the answer is:
remark
'comment' is the definition.
(a remark is a spoken comment)
'about blemish' is the wordplay.
'about' becomes 're' (regarding).
'blemish' becomes 'mark' (mark is a kind of blemish).
're'+'mark'='REMARK'
(Other definitions for remark that I've seen before include "Notice; happen to say" , "Comment or mention" , "Written or spoken comment" , "Something said; take notice of" , "(E.g. Virgil's) pastoral poems" .)