Why does some ice look blue?
and some ice looks white?
It turns out that it all has to do with the frequencies of light absorbed by water molecules. The vibrational modes that are absorbed by the O-H bonds in water fall in the red end of the visual spectrum. So water absorbs red light and blue is transmitted. But we only see it if the ice is sufficiently thick and the light is passing through the ice so as to absorb more red and transmit more blue.
For once, vibrational spectroscopy is useful.