Pink slate (5)

I believe the answer is:

knock

I believe this is a double definition.

'pink' is the first definition.
(both can mean to hit or strike)

'slate' is the second definition.
(both can mean to criticise)

(Other definitions for knock that I've seen before include "Criticise; rap" , "Tap on door" , "Setback; thirteen across" , "Find fault with" , "Bash" .)

I've seen this clue in The Times.

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