Dishonest as a redhead or brunette? (6)
I believe the answer is:
unfair
'dishonest' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for unfair that I've seen before include "Not cricket?" , "Foolishness" , "raining perhaps?" , "out of order" , "Not equitable-or blonde?" .)