Answer:
1. Clouds are made up of tiny water droplets or ice crystals, usually a mixture of both. The water and ice scatter all light, making clouds appear white. If the clouds get thick enough or high enough all the light above does not make it through, hence the gray or dark look.
2. Clouds move because the wind is carrying the parcel of cloudy air along. The droplets in the cloud are moving fast with the wind, but new cloud drops are always forming in the same place where the air is pushed up near the hill, so the front of the cloud appears stationary.
