What a heavenly colour! (3,4)

I believe the answer is:

sky blue

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'what 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 believe this answer much more).
'colour' becomes 'blue' (blue is a 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" , "Azure" , "Heavenly shade" , "Seeing this, one may be looking up" , "Shade (seen above?)" .)

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

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