Blue, extremely shabby clothing for dog (6)
I believe the answer is:
smutty
'blue' is the definition.
(thesaurus)
'extremely shabby clothing for dog' is the wordplay.
'extremely' suggests removing the centre.
'clothing for' is an insertion indicator.
'dog' becomes 'mutt' (mutt is a kind of dog**).
'shabby' with its centre removed is 'sy'.
'sy' placed around 'mutt' is 'SMUTTY'.
(Other definitions for smutty that I've seen before include "Rather rude" , "Filthy" , "Rather indecent" , "Improper" , "Blue" .)