Craig Young

The sky appears blue to us because of the way light from the Sun passes through our atmosphere.  Earth's atmosphere is composed of nitrogen (78%), oxygen (21%), argon (about 1%), and other gases.  Different frequencies (colors) of light interact differently with those gases.  When blue and violet light bounce of the molecules of those gases, the light scatters in all directions.  Other frequencies of light are less affected by the atmosphere.  If the light didn't scatter, the sky would appear black except when looking directly toward the Sun.  But, since the blue and violet light scatters in all directions, it enters your eyes not matter which direction you are looking.  Since our eyes are not very sensitive to violet light, the predominant color we perceive is blue.

If there is more water vapor or smoke in the air, other frequencies of light are also scattered, and we get a variety of frequencies of light hitting our eyes.  When that happens, our brains interpret that as white.  Which is why clouds appear white and foggy/smoggy skies are whitish.

The sky has its own sin color dont use this type of question if you are trying to imply something inapropriate