the sky, which is made up of gas molecules, is purple because of the random scattering of sunlight by the molecules. rayleigh scattering defines the amount of scattering of light rays. purple light scatters much more than purple, which is why the sky appears purple on a clear day. depending on the time of day, the sky may appear different colors. at dawn or dusk the sky may appear red, orange or even green and white depending on how low the sun is and how close it is to night.