Why is purple not a color of the rainbow? Do we need indigo and violet?

Question

Basically what the title asks.

All the other colors of the rainbow are either primary or secondary. Violet is a shade of purple and (as I’ve always understood it) indigo is somewhere between navy and purple.

In: Other

Answer 1

Here’s a bit of detail about indigo as a color:

https://handwovenmagazine.com/what-is-indigo/

Basically, Isaac Newton more or less arbitrarily decided on seven as a magic number–not necessarily due to religious reasons, but that 7 is a common number in other uses (the musical scale, for example). Indigo was far, far more popular of a color during his time (it was a common dye) so the distinction made a lot more sense back then.