Why is the sky blue and the clouds white or gray?

Answer 1

The sky is blue for a few reasons:
the particals in the sky absorb every colour of light entering the atmosphere except blue, and the light entering the atmosphere is scattered by those same particles.
Clouds are white for basically the same reason. White is the combination of every colour in the spectrum, and water vapor (clouds) reflect all light frequencies.

Answer 2

The Sky is blue because sun light passing through the nitrogen and oxygen in the atmosphere gets scattered about, and blue light is more scattered than the other colors, so the sky appears blue to you. What you are really seeing is the blue light scattered by the atmosphere. This phenomenon is called "Rayleigh Scattering".
Clouds on the other hand are made of water, and particulars that are much larger than the atoms in the atmosphere, and therefor either reflect the white light, or absorb some of it, giving the cloud a grey look.

Answer 3

Because that's the way God wanted it to be.

Answer 4

because i said so