When you see them in real life, the Northern Lights aren’t actually very colorful at all. They often appear milky white in colour, “almost like a cloud,” as one seasoned traveller puts it. He says he often sees them as mostly white, with faint hints of red and pink.
“The discrepancy occurs because the specific cells that our eyes use to detect light at night also happen to be terrible at detecting colour. For that reason, auroras often appear only in shades of grey.”
Dr. Andrea Thau, vice president of the American Optometric Association (huffpost.com)