The sun's rays hit the Earth's atmosphere, where the light is scattered by nitrogen and oxygen molecules in the air. The blue wavelength of this light is affected more than the red and green wavelengths, causing the surrounding air to appear blue.
"The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.
However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue." Read More >>> http://www.sciencemadesimple.com/sky_blue.html
5 months ago
Last edited at 7:57PM on 1/22/2013
it is basically due to the components or chemicals present in the sky in which each of those chemicals absorbs colors in the light spectrum and the color or combination of colors it reflects is the color we see. There are various chemicals so the resultant overall color is the combination of all the reflected colors by those chemicals individually.
Similar to the question of why are red apples red :)