Pop quiz hot shots: if you ever find yourself on a glacier hike in New Zealand (and you should, it’s great fun!) what makes the ice blue instead of the white we’re used to?
Answer: it depends on the light that’s reflected. Atoms interact with wavelengths of light differently causing some to be reflected and some to be absorbed, so for example something is black when it absorbs all the light hitting it (and why black objects get hot!). Everyone’s favorite life-sustaining molecule, H2O, vibrates in a way that absorbs light towards the red side of the spectrum, leaving the blue color you see above.
So why is ice and snow usually white then? For the simple reason that virtually all the light you see hitting a snowy surface is scattered a few times and eventually reflects back, giving white, and this overwhelms the faint blue color water normally has. It’s only when the light is absorbed by the water (you usually need around a meter of it) that the blue makes it through, similar to how coffee looks light when poured but much darker in a cup.
And that is why glaciers look so damn cool. The more you know…