Rich colour (not black) (4)
I believe the answer is:
lush
'rich' is the definition.
(similar in meaning)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lush that I've seen before include "Slang drunkard like rich growth" , "Of grass, growing thickly and strongly" , "Succulent - soak" , "sponge" , "Growing luxuriantly, grass say" .)