​The picture above came from https://aurorasaurus.org/learn_more#aurora-colors

What the Color Means

As you probably know, the aurora can be green but there are many more colors that it can be like having red, blue, violet, pink, and even white depending on the altitude that it occurs and what element becomes excited

As you might have guessed there is quite an exciting science that causes the aurora. according to NASA's "Aurora" 2003 document, typical auroras come from fast-moving electrons from space with the oxygen and nitrogen in Earth’s upper atmosphere. The electrons—which come from the Earth’s magnetosphere, the region of space controlled by Earth’s magnetic field —transfer their energy to the oxygen and nitrogen atoms and molecules, making them excited. As the gases return to their normal state, they emit photons, small bursts of energy in the form of light. When a large number of electrons come from the magnetosphere to bombard the atmosphere, the oxygen and nitrogen can emit enough light for the eye to detect, giving us beautiful auroral displays. If oxygen is excited at a high altitude it will show red if at lower altitude it will be yellow or green.  If it is nitrogen, it will be blue, but can be combined with red to show a purple This light occurs at altitudes of 60 to more than 250 miles. 
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The picture above is from www.gi.alaska.edu/monitors/aurora-forecast