Badly off colour? (6)

I believe the answer is:

unwell

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'badly off colour?' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?

This is all the clue.

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(Other definitions for unwell that I've seen before include "Indisposed" , "Poorly" , "Sick, not in good health" , "Ill, not in good health" , "Off-colour" .)

I've seen this clue in the Evening Standard.

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