The bombarded atoms and molecules consequently give off light of their own characteristic color. The same phenomenon can be seen every night in the city. The color given off depends entirely on the gas contained within the bulb. This is exactly what happens in our atmosphere. The colors seen in a display of the northern lights depends on the elements being stimulated.
Atomic oxygen produces a yellow-green color, and at extremely high altitudes a red color.
Molecular oxygen and nitrogen also produce a red color. Very high displays have a bluish or purplish tint due to ionized molecular nitrogen receiving sunlight. Also, just as the brightness of a light bulb depends on the amount of electricity being supplied to it, so does the brightness of an aurora depend on the energy of the charged particles bombarding the atmospheric elements. In addition, auroras are not only fascinating to watch because of their varying colors, but also because of the many shapes that can be manifested. The shape completely depends on the fluctuations of the earth's magnetic field.