He changes colour and sounds dreadful (4)
I believe the answer is:
dyer
'he changes colour' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'sounds dreadful' is the wordplay.
'sounds' indicates a 'sounds like' (homophone) clue.
'dreadful' becomes 'dire' (synonyms).
'dire' is a homophone of 'DYER'.
'and' is the link.
Can you help me to learn more?
(Other definitions for dyer that I've seen before include "Person colouring cloth" , "Colour-changer" , "Cloth worker" , "Adder of colour" , "One colouring cloth" .)