A colour of historic eminence (4)

I believe the answer is:

grey

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

I cannot understand how the remainder of the clue works.

(Other definitions for grey that I've seen before include "Lady Jane --" , "The colour of ash" , "Anonymous" , "Drab colour" , "showing his age?" .)

I've seen this clue in the Evening Standard.

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