Light is made up of all the colors, agreed? Well, the sky appears blue because of 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.
The Sky looks like it's Blue because air (Earths Atmosphere), scatters shorter blue wavelengths more than it does Red longer ones. The process is called; Rayleigh scattering, and also is why Sunsets are are Red.