Colour left unknown in card game (6-3)
I believe the answer is:
twenty-one
'card game' is the definition.
(I know that twenty-one is a card game)
'colour left unknown' is the wordplay.
I cannot quite understand how this works, but
'left' could be 'went' (left can mean went away) and 'went' is found in the answer.
'unknown' could be 'y' (algebra) and 'y' is found within the answer.
'colour' could be 'tone' (tone is a kind of colour) and 'tone' is located in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for twenty-one that I've seen before include "Target total in blackjack or pontoon" , "XXI - used to be the coming of age year" , "Card game, blackjack or pontoon" .)