It is sad; tragic really: I now have to file the color of light known as “purple” into the same folder as Santa Claus and the Easter Bunny. I recently attended a seminar by Joe Bokelman of ETC, who made the comment that the straight line cutting through the bottom of the CIE 1931 color space is known as the “line of purples”, because purple light doesn’t really exist. It is an illusion of additive color perceived by the human eye.
I think most lighting professionals perceive that white light is an illusion, the result of additive mixing of the visible spectrum. But I never stopped to think that “purple” was not a primary color of the rainbow, but rather the mix of the opposite ends of the spectrum.
It is also counter to most people to realize that amber and indigo (royal blue) mix to produce purple, too. A good example is the Purple Rain poster above; the purple light in the fog is actually the combination of blue and amber. Of course, Prince and his bike are actually decked out in purple. You know, the subtractive kind.