h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I personally think that Indigo is made up. As far as I can see with my naked eyes, the Indigo/Violet bit takes up about the same angular interval as the other five colours, so why not just call it Violet? We could always modify the popular mnemonic phrase, thus:
'Richard Of York Gave Battle Vainly'.

I also once saw a complete rainbow, which you can if you're in a plane and the sun has risen above the clouds. It was actually a complete circle, which was a total revelation to me, and I thought it most beautiful.

In the version of the song about a rainbow that I've heard, there's no Indigo anyway!

It goes 'red and yellow and pink and green, orange and purple and blue... I can see a rainbow, see a rainbow, see a rainbow too!'

Or is that just the easy kids version?

It was on my Sooty video (which I must find again, I love that!)

Yes, when I did physics at school, it was mentioned that Indigo was almost certainly made up just because 7 colours was considered a pleasing number.

It makes more sense that there are only six colours, as that explains paint colour mixing better - red and yellow make orange, yellow and blue make green and blue and red make purple.

Newton and his contemporaries were highly attuned to the colour indigo, as it was the colour of the ink they used. It sometimes seemed to scholars of those days that all the world was paper, and all the sea was ink.