The blue colour of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of 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 one looks, one sees some of this scattered blue light.
Since, one sees the blue light from everywhere overhead, the sky looks blue.