At snooker, not a colour (3)
I believe the answer is:
red
'a colour' is the definition.
(red is a kind of colour)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for red that I've seen before include "- Cross; - carpet" , "socialist?" , "Blushing" , "Stop light" , "- - poker: Kniphofia" .)