Fine shade of blue (3)

I believe the answer is:

sky

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'shade of blue' is the definition.
(I've seen this in another clue)

I can't explain the rest of the clue.

(Other definitions for sky that I've seen before include "Hit (a ball) very high" , "Outer space viewed from earth" , "Orbiting space-station" , "Weather" , "Hit high into the air" .)

I've seen this clue in the Evening Standard.

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