3. Colors Depend on Atmospheric Gases
The green color in auroras is produced when charged particles collide with oxygen molecules at altitudes of approximately 60 to 120 miles (100 to 200 kilometers). At higher altitudes, above 120 miles (200 kilometers), oxygen atoms emit red hues. Nitrogen molecules, when excited, can produce blue or purple colors, depending on the altitude and energy levels involved. For more details, refer to NASA’s explanation: NASA Science: Auroras.