A heavenly colour (3,4)

I believe the answer is:

sky blue

I'm a little stuck... Click here to teach me more about this clue!

'a heavenly colour' is the definition.
(I've seen this before)

'heavenly colour' is the wordplay.
'heavenly' becomes 'sky' (I can't justify this - if you can you should give a lot more credence to this answer).
'colour' becomes 'blue' (blue is a kind of colour).
'sky'+'blue'='SKY-BLUE'

Can you help me to learn more?

(Other definitions for sky blue that I've seen before include "Heavenly colour" , "Pale colour -- buy elks (anag)" , "Colour overhead on a fine day" , "Coventry City footballer" , "Heavenly shade" .)

I've seen this clue in the Evening Standard.

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