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Comment by LatteLazy | Hacker News Reader

There are "7" colours in the rainbow because Newton said so. He said that because 7 is a biblical number and he was really really into biblical numerology.

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Newton gave it: red, orange, yellow, green, blue, indigo and violet

Imho, indigo and violet are the same thing (at least very close), and cyan is missing, so red, orange, yellow, green, cyan, blue, violet would have made more sense

But of course it's indeed quite possible the language shifted and it made sense in Newton's time

Imo cyan and blue are a lot closer than indigo and violet

To me cyan looks blue-green, really in the middle but also significantly lighter than blue, while indigo and violet both look purple-like

I'm not a native English speaker though, and as far as I know neither cyan nor indigo are commonly used in standard everyday language, but more in their own niches (printing, clothing, ...)

The reason there is violet, by the way, is that the eye's red receptors weakly respond in that range, causing a perception of red to creep into the blue.

I thought that was because he wanted/believed in a correspondence between colors and music, and the scale had seven main notes, A-G (the white keys on a piano). Also note that this scale is called the https://en.wikipedia.org/wiki/Chromatic_scale, which is surely not a coincidence.

Why not both!

The chromatic scale is when you play all 12 semitones. You're thinking of a C major scale.

The wiki article gives the following etymology:

> The word chromatic comes from the Greek chroma, color; and the traditional function of the chromatic scale is to color or embellish the tones of the major and minor scales.

But this feels a bit weak to me. Would be nice to have a more authoritative source.

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