Rat's characteristic yellow pigment (7)

I believe the answer is:

traitor

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'rat's' is the definition.
(I've seen this in another clue)

'characteristic yellow pigment' is the wordplay.
'characteristic' becomes 'trait' (a trait is a quality or characteristic).
'yellow pigment' becomes 'or' (I can't explain this - if you can you should believe this answer much more).
'trait'+'or'='TRAITOR'

Can you help me to learn more?

(Other definitions for traitor that I've seen before include "Rat riot (anag.)" , "One committing treason" , "One betraying one's country" , "Maclean was one" , "Backstabber" .)

I've seen this clue in The Guardian.

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