Clouds are white for the same reason as ice. They are composed of water droplets or ice crystals mixed with air, very little light that strikes them is absorbed, and most of the light is scattered, appearing to the eye as white. Shadows of other clouds ab
White-water rapids is my guess, but the original website is a 404 error page, and so far the pinners I've checked haven't listed what it is, except snow. The motion doesn't seem to correlate with snow.