Blue colour of the sky is due to
Scattering of light
The amount of scattering that occurs is dependent upon the frequency of the light. So as white light from the sun passes through our atmosphere, the high frequencies become scattered by atmospheric particles while the lower frequencies are most likely to pass through the atmosphere without a significant alteration in their direction. Compared to blue light, violet light is most easily scattered by atmospheric particles. However, our eyes are more sensitive to light with blue frequencies. Thus, we view the sky as blue.