Yes actually, I know exactly why it is blue and not any other color. It is in fact due to a process called Rayleigh Scattering, wherein the visible wavelengths with higher energies, I.e., the shorter wavelengths are scattered more readily by the molecules of air in the atmosphere... visible light wavelength of purple is scattered way up in the upper atmosphere so no purple enters the retina of humans.. but blue light wavelengths is just right so as to scatter alll about in the atmosphere by the molecules of air, and enter our retina as blue and not white.