Indigo...

So I've been tripping on colors lately, and what's kept bugging me was how in America we count seven distinct colors, including what we call 'indigo.' Between the other primary colors we only count one, between red and yellow we take note of orange, between yellow and blue we take note of green, but then between blue and red we note not just purple, but indigo. I figured it had to be a cultural thing, and it seems that I was right in that assumption. Below is a link that I though was fun and educational.

http://hypertextbook.com/physics/waves/color/