Nothing but blue skies

During this fine weather I am making a point of admiring the sky. It is a deep, rich, forget-me-not blue. An unfamiliar colour, I reflect. Looking west towards the Cook Strait, where the Air New Zealand jets are routed, I can see a few wisps of high cloud. Man made cloud.
Overhead and in all other directions, an intense blue.
In Europe there is always a whitish haze these days. Jets dashing hither and thither filling the stratosphere with water vapour. So much that "sky blue" is a pale and washed out hue.
Despite what seems like a lot of internal flights, the skies here are almost empty. You never look up and see a mile high plane, winging it's way, maybe from Prague to Boston, as you would in the UK. NZ is not en route from anywhere to anywhere other than the Antartic - not, mercifully, known for its international airports.
And that, I conclude, is the reason for the blueness of the heavens.