Like diamonds, suitably? (3)

I believe the answer is:

red

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'like diamonds' is the definition.
(I've seen this in another clue)

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

(Other definitions for red that I've seen before include "Primary colour" , "14 -- breed of 4" , "Colour of communism" , "Very angry, seeing this" , "Bloodshot" .)

I've seen this clue in the Evening Standard.

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