system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is snow almost a solid white, while other frozen forms of water are clear?
gpt
Snow is a whole bunch of individual ice crystals arranged together. When a light photon enters a layer of snow, it goes through an ice crystal on the top, which changes its direction slightly and sends it on to a new ice crystal, which does the same thing. Basically, all the crystals bounce the light all around so that it comes right back out of the snow pile. It does the same thing to all the different light frequencies, so all colors of light are bounced back out. The "color" of all the frequencies in the visible spectrum combined in equal measure is white, so this is the color we see in snow, while it's not the color we see in the individual ice crystals that form snow.

Basically, if you just had a big block of ice, light can pass right through it, where as with snow, light is being reflected and bounced around many many times, through many crystals of snow.