Why are clouds white?

Answer 1

The same question could be asked about a field of snow, a bowl of sugar or the hair on a polar bear. All the individual elements in these, as with the water droplets/ice crystals in a cloud, are transparent and yet together they appear white.

White light from the sun is scattered when it hits the water droplet/sugar grain/ice crystal. The large number of water droplets scatter the light in all frequencies so it emerges as white light and the cloud appears white. In deep clouds, the light is scattered out of the cloud and as you get deeper into the cloud more and more light is scattered so little reaches the bottom. This is why the bottom of a cloud appears grey or sometimes nearly black