One using colours of very poor quality, reportedly (4)
I believe the answer is:
dyer
'one using colours' is the definition.
(someone dyeing things different colours)
'of very poor quality reportedly' is the wordplay.
'of very poor quality' becomes 'dire' (I've seen this before).
'reportedly' shows a homophone (sound like).
'dire' is a homophone of 'DYER'.
(Other definitions for dyer that I've seen before include "One colouring cloth" , "Brunette trying to be blonde" , "Drey (anag.)" , "Colourer (of clothes, perhaps)" , "Increase (in output)" .)