NB, this is the Off-topic forum, before anyone complains!
Last night I was at my choir and 'blue sky' featured in one of our songs, and without thinking my brain disambiguated it to 'clear sky' and I sang it.

Luckily, it was only a practice.
Why does getty have 'clear sky' rather than 'blue sky' (which surely most people say) anyway? Hypothetical question!!!