Colour that would run? (6)

I believe the answer is:

yellow

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'colour' is the definition.
(I know that yellow is a type of colour)

I don't understand the remainder of the clue.

(Other definitions for yellow that I've seen before include "Colour between orange and green in the spectrum" , "Sunny colour" , "Cowardly (colloq.)" , "Name of river" , "Custard-coloured" .)

I've seen this clue in The Globe and Mail and The Irish News.

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