Why is ice colourless while snow white if they are both solid form of water?

Answer 1

All of them are colourless, it's just the way they reflect light, along with the density.

Answer 2

Snow looks white because of the air trapped in it. If you look at snow flakes under a good microscope, they are transparent, like ice.
If you look at the ice cubes in your refrigerator, you may find that some of them are clear and some are white, also from air traped when the water froze. If you want to make clear ice cubes, freeze them, let them melt, and carefully freeze again. The freezing process "squeezes" the air out of the water (sort of). It actually has to do with the soluability of gas in liquid water vs solid water.