Not exactly vivid, but arguably colourful! (5)
I believe the answer is:
livid
'colourful' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I can't see?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for livid that I've seen before include "Furiously angry, the colour of lead" , "in a paddy" , "Spitting blood" , "Black and blue" , "Black-and-blue - furious" .)