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Comment by theaeolist | Hacker News Reader

Is there any colour (by hue) not in the rainbow?

I don't know about 'by hue' but almost all colors are not in the rainbow. The spectral locus is a line that runs around the edge of a 2D color space (technically 3D if you include luminance as well...).

7D if you are a mantis shrimp.

> 7D if you are a mantis shrimp.

Don't be sure:

* https://www.popsci.com/blog-network/ladybits/mantis-shrimp-v...

* https://phys.org/news/2014-01-mantis-shrimp-vision-different...

Though they do see polarization, which is a neat feature.

Pink is considered to be a color not in the rainbow.

http://aschoonerofscience.com/science-communication/the-phys...

I’ve seen this before and am still bothered by the color name chosen. Is calling magenta “pink” a British (or Australian) thing maybe? Pink is a pale red. [1] Magenta isn’t pale red. Even the color wheel used here doesn’t label it pink. Where does this come from?

But yes, it’s interesting to learn that there is no wavelength for magenta.

[1] https://en.m.wikipedia.org/wiki/Pink

I think it's a British thing possibly, we have a children's nursery rhyme that includes the colour pink so that might be the reason as we just get used to calling it pink as a kid.

That wiki page says the Odyssey is written in approximately 800BCE. It looks more violet than pink to me.

The pure purples are not in the rainbow because they are a mixture of red and blue, whereas the rainbow is made of single-frequency colors.

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