I’ve done a study of color recently. Fascinating subject! Did you know people can distinguish something like 10 million different colors? (The full size version of this picture contains 1 million pixels, each little dot a different color.)

There is something very mysterious about the color purple.
It is the color of royalty. It is both sensual and spiritual.
It is the only “non-spectral color” amongst the major colors of the color wheel. The spectrum (colors of the rainbow) run Red, Orange, Yellow, Green, Blue, Indigo, Violet – we learned the acronym Roy G Biv to remember that when I was growing up, but Indigo and Violet are omitted when it is turned into a color wheel. (Color wheels are used by artists to work out color combinations.)
Of course the spectrum is a line. It is actually a gradient scale of frequencies or wavelengths. Red is the shortest visible light waves (any shorter and you get “infrared” which you can feel as heat but is not visible) and violet the longest (beyond which you get “ultraviolet”, again not visible to the human eye).
The color wheel is a circle which raises the question: how do you turn a line into a circle? By connecting the ends in between. And what do you connect them with? Purple,
If you mix red and yellow you get orange, which is in between them on the spectrum and on the color wheel.
If you mix yellow and blue you get green, which is in between them on the spectrum and on the color wheel.
If you mix blue and red you get purple, which is in between them on the color wheel. But there is no “in between” red and blue in the spectrum.
Purple is a non-spectral color.
The mysterious color purple.