You see, while sunlight appears to be white, it is actually made up of many different colors. This colored light travels in waves, as all light energy does, and each wave is a different length. As sunlight enters the Earth's atmosphere, it is scattered in all directions by gas particles that reside there. Blue light is scattered more so than the other colors because it has the shortest wavelength. Whereas colored light of longer wavelengths, such as red, orange and yellow, tends to pass through the atmosphere unaffected. This is why we see the sky as blue, and it's just as well because a yellow sky wouldn't be quite right. At least not in our opinion!