Earth receives most of the light from the Sun and earth atmosphere scatter Blue color the most (red the least) and compare to any other color and thats the reason why we see the atmosphere which covers the sky as blue.
Many a times we see the sun and nearby area as red mostly in the morning or at the time of sunset because of the fact that most of the blue light has been scattered by the atmosphere as the distance of the sun in the morning or evening is little more then normal.
