Dodge a bomb. It's a blue! (4,3)

I believe the answer is:

duck egg

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'a blue' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see a link between them that I don't see?

'dodge a bomb' is the wordplay.
'dodge' becomes 'duck' (to dodge is to duck or avoid).
'a bomb' becomes 'egg' (informal term for a bomb).
'duck'+'egg'='DUCK EGG'

'it's' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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