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It's a fascinating phenomenon, right? Worth noting the "blue" in both those examples comes from physics not pigments.

The reason pigments or anything else is blue is also because of physics.

A friend of mine once claimed that the sky wasn't blue. I challenged him, expecting some argument about physics and Rayleigh scattering.

Instead he looked at me and, with a straight face, said "it's the spy satellites which are blue. And there are very many."

While true, it might be worth noting that if you grind iridescent blue material it will loose its color. Pigment will not.

Water is "actually" blue, as in due to the chemistry of its electronic configuration. A deep column of water has a blue color in a way that other liquids, such as benzene, do not. There was a cool picture of this demonstration in one of my old chemistry books.

https://en.m.wikipedia.org/wiki/Color_of_water

Reflection of the sky accounts for much of the color of natural bodies of water, but it's cool to know that it's blue even in the absence of blue reflection.

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