Although you can spot many colors of stars in the night sky, purple and green stars aren't seen because of the way humans perceive visible light.

There are red, orange, yellow, blue, and even white stars, but no green or purple stars.

Green and purple stars do exist. The color of stars depends on their temperatures, and they emit radiation throughout the visible spectrum. But when a star emits peak radiation at a wavelength we define as green, it also emits radiation over the rest of the spectrum. Green is in the middle.

Although our limited eyes cannot detect purple stars, the color purple is nevertheless part of a skywatcher’s vocabulary. It becomes especially noticeable when we deal with atmospheric aberrations, lensing effects, and the scattering of light.