Depressed surface for putting on mix of colours (9)

I believe the answer is:

bluegreen

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'mix of colours' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'depressed surface for putting on' is the wordplay.
'depressed' becomes 'blue' (I've seen this in another clue).
'surface for putting' becomes 'green' (I am not sure about this - if you are sure you should believe this answer much more).
'on' says to put letters next to each other.
'blue'+'green'='BLUEGREEN'

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I've seen this clue in The Times.

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