We don't tend to think too much about the clouds drifting overhead, but what causes their coloration is more complex than you may think.

Clouds get their color due to light from the sun being white. As light passes through a cloud, it interacts with water droplets, these are much larger than the atmospheric particles that exist in the sky.

When sunlight hits particles in the atmosphere, blue light is scattered away stronger than any other color because of its shorter waves. This gives the impression that the sky is blue.

Whereas in a cloud, sunlight becomes scattered by bigger water droplets which scatter colors equally resulting in sunlight remaining white in appearance.

Sometimes when clouds are grey, this is caused by the same scattering that results in them being white.

When light is scattered in a cloud it is usually sent back upwards, out to the sides of the cloud, leaving the tops and sides of the cloud whiter than the base which receives less light.

At sunrise or sunset, clouds may take on a red or orange color due to sunrise and sunset. The sun is very low in the sky and so light must travel through more of the atmosphere. As a result, more blue light is scattered and deflected away which allows more red and yellow light to reach the earth.