Ice-boy: here is the answer, which I agree with 100%:

*"The sky is actually colorless. The color you see is actually sunlight being diffracted by the gases in our atmosphere. On a clear (non-hazy, non-polluted) day, the sky appears blue. This is due to the high concentration of Nitrogen. However, in a smog clogged city, the sky can appear white to dirty brown. This is due to the high concentration of hydrocarbons. You can even get a red-orange sky if you're near a large fire or if a large volcano has just erupted."

*And it was found with one google hit.