[Bob_Sheep]

I couldn't take the article seriously after the suggestion that he was producing colours that are not seen on a natural rainbow and that the rainbow is wrong. The spectra for sunlight is almost complete in the visible region apart from a few small gaps where various elements absorb the light. If you look at a proper spectrum for sunlight you can clearly see the colours he claims are missing.

[Terr_]

Natural rainbows are INCOMPLETE because a prism splits light into SINGLE isolated wavelengths. Can you name the wavelength of magenta in nanometers?

Colors arise from the presence (and absence) of 1...N simultaneous wavelengths triggering a suite of inexact biosensors.

If you ever see magenta in a natural rainbow, it's only because there are two-or-more spectrums are overlapping in a messy and inexact manner.

TLDR: "Color" is to "wavelength" as "taste" is to "chemical".

[zokier]

Purple (distinct from violet) does not appear on natural rainbows.

[Zancarius]

This reminds me of the scuffle about pink. I can't find the original article linked to from HN, but a quick search yields some interesting disputes:

http://newsfeed.time.com/2012/03/07/does-the-color-pink-exis...

http://gizmodo.com/if-the-color-pink-doesnt-scientifically-e...

http://blogs.scientificamerican.com/observations/2012/03/05/...

If there's one saving grace, I suppose it's that we're not tetrachromatics, right? ;)

[mark-r]

But some women are...

http://discovermagazine.com/2012/jul-aug/06-humans-with-supe...

[Zancarius]

Do be aware that it looks like it's an area that needs further study (and apparently the "fourth" cell may detect light between red and green). On average, humans are (generally) not tetrachromats. Poking around on a cursory search suggests that only one subject in that 2012 study expressed attributes that were definitive evidence of the existence of tetrachromacy in humans. Apparently there's some ongoing discussion as to whether or not the optic nerve is capable of funnelling an extra color channel to the brain, so that'll be of interest to follow.

Importantly, I was thinking along the lines of some insects and spiders that are capable of seeing into the UV spectrum for sexual signalling or locating food sources (e.g. flowers). Which reminds me that there's been some evidence that suggests those who've had cataract surgery may be able to see deeper into the violet spectrum without a UV-filtering obstacle in place. But that's likely just the function of the blue-sensitive cells.