Colourful line - but it sounds dire! (4)
I believe the answer is:
dyer
'colourful line but it' is the definition.
I can't judge whether this definition defines the answer.
'sounds dire' is the wordplay.
'sounds' indicates a 'sounds like' (homophone) clue.
'dire' is a homophone of 'DYER'.
Can you help me to learn more?
(Other definitions for dyer that I've seen before include "Also a cleaner, probably" , "Changer of colour" , "colourist" , "Adder of colour" , "He changes colour, as it were" .)