Unjust brunette? (3,4)

I believe the answer is:

not fair

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'unjust' is the first definition.
(I've seen this in another clue)

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

Can you help me to learn more?

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