Counterblast violently eradicates contrast colour? (4)

I believe the answer is:

blue

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'colour?' is the definition.
(blue is a colour)

I can't explain the rest of the clue.

(Other definitions for blue that I've seen before include "Top sportsman who's up" , "ball at snooker" , "Miserable - cerulean" , "and 17 World's largest mammal" , "Sad, melancholy" .)

I've seen this clue in The Irish Times.

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