Not in the pink - blue (3-6)

I believe the answer is:

off-colour

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'blue' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for off-colour that I've seen before include "Not in the pink?" , "Unwell or indelicate - a bit pale?" , "Unwell, lacking pigment?" , "Not well - looking pale" , "Rather poorly" .)

I've seen this clue in the Evening Standard.

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