Colors
What Causes the Aurora's different colors?
The specific colors see by us when we view the
aurora, depend on the specific atoms and their level of
energy.
At high altitudes where the aurora is found the air
consists of atoms of molecular oxygen and nitrogen.
The electrons of the aurora, when greatly excited can split
these atoms apart thus emitting typical colors corresponding
to molecular oxygen and nitrogen.
oxygen atoms= green and red
Nitrogen atoms=blue and purple
http://www.princesslodges.com/blog/index.php/fairbanks-princess/alaska_northern_lights/