Hmm... sounds correct I think. Just reinforce a bit from my
understanding.
Clouds that are grey contain a larger amount of water which will be
able to block or absorb some of the sunlight. With a larger amount
of water, there is probably also more particles in the water that
also serve to block the sunlight. White clouds appear white because
there is less water to block the sunlight.
As for the red cloud, it is like what is said in the wikipedia link
posted in one of the post. It is due to light scattering and
probably involves diffraction where light is bend (as in the prism
effect u have mentioned). I would think that the moonlight, which
we all know is light reflected on the moon from the sun, does
attribute to the colour of the clouds.
