Colour of pure diamond (3)

I believe the answer is:

red

'colour' is the definition.
(red is a kind of colour)

'of pure diamond' is the wordplay.
'of' indicates the answer is hidden within the clue.
'RED' is hidden within 'pure diamond'.

(Other definitions for red that I've seen before include "Colour of garnets" , "Colour for danger" , "eg Cardinal" , "Colour of a cardinal's hat" , "Blood-coloured" .)

I've seen this clue in the Evening Standard.

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