Question: why are clouds white ?

Sean Murphy answered on 16 Mar 2012:

In much the same way as why skies are blue, clouds are white because their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths (red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light. Clouds will appear dark or gray when either they are in another clouds shadow or the top of a cloud casts a shadow upon its own base.