Dreadful-sounding colourist (4)
I believe the answer is:
dyer
'colourist' is the definition.
(I've seen this before)
'dreadful-sounding' is the wordplay.
'dreadful' becomes 'dire' ('dire' can be a synonym of 'dreadful').
'sounding' shows a homophone (sound like).
'dire' is a homophone of 'DYER'.
(Other definitions for dyer that I've seen before include "One changing colour" , "Person colouring materials" , "Increase (in output)" , "He changes colour, as it were" , "Cloth-stainer" .)