On nice days the clouds are white and make cool shapes. When it's going to rain the clouds are dark grey. When it's sunny outside the clouds look white and puffy. On a rainy, cloudy day the sun is behind the clouds. The dark rain clouds have lots of rain drops in them.
Gravity makes the raindrops fall .
It pulls them down. I think scientists use the clouds to predict the weather by looking at their shape, size, color, and position. For example if there were black clouds it would probably rain that day. They are just some examples. Some of the clouds are white.