Look closely at a rainbow, and you’ll spot red, orange, yellow, green, blue, and violet, but not purple. That’s because every color in a rainbow corresponds to a single wavelength of light.

"Our room temperature solid-state maser amplifier avoids ... purple," lead author Tom Day explained. "The purple color is ...

The human eye does not actually see purple ... by a wavelength of light, and the strength of the signal from each cone (and type of cone). The brain then determines what color you are looking ...