NPR books did a brief review of Jude Stewart's book, Roy G. Biv: An Exceedingly Surprising Book About Color,

HERE.

One of the more interesting evolutions of our perception of the color spectrum is that there are actually only 6 colors in a rainbow. Sir Issac Newton, unpon his observation of the spectrum, was pressured to add Indigo, to make the total colors 7, which matched a musical scale. Which of course had nothing to do with science or accuracy, but today we accept it!

The Article takes five minutes or less to digest. I recommend it.

My Best,

Gary