Isn't the colour indigo named after the colouration indigo? If not, it should have been. "But scientifically the different colors of the rainbow have different wavelengths." This is absolutely true, but there is a LOT to it. It's not like there is an exact wavelength "x" where x is one colour and x-1nm is another. You might be able to say that for yourself, perhaps, but a) perhaps not and b) your limits would not agree with other people, especially those from other cultures ( https://www.sapiens.org/language/color-perception/ ). I bring up "indigo," because I don't recall ever getting that response to the question "what colour is this?" People say "blue," or "purple," or, rarely, "violet." And, on top of all of that, the colours we see in the real world are almost never pure wavelengths. You can't find a natural object out there anywhere that reflects only one wavelength of light and absorbs the rest. What colour is grass? "Green," one would say, but chlorophyll reflects light with wavelengths from 450 nm to around 650 nm pretty much equally. If you take the midpoint/average of that, it'd be around 550 nm, which is more yellowy than greeny, but, since the human eye is more sensitive to green light than to yellow light, our perception of it is more green than yellow.

Wavelength Red ~ 700 - 635 nm ~ 430 - 480 THz Orange ~ 635 - 590 nm ~ 480 - 510 THz Yellow ~ 590 - 560 nm ~ 510 - 540 THz Green ~ 560 - 520 nm ~ 540 - 580 THz Cyan ~ 520 - 490 nm ~ 580 - 610 THz Blue ~ 490 - 450 nm ~ 610 - 670 THz Violet ~ 450 - 400 nm ~ 670 - 750 THz Seems pretty cut and dried to me, not really open to interpretation or cultural differences

Indigo dye is named after the very dark blue color indigo, but when you put a drop of it in a bundle of cotton material it is diluted and turns a light 'faded blue jean' color that is also called indigo after the name of the dye but it is not the same dark inky blue of the color indigo.

Ironic that Indigo is not on your list. Where did you find those? I typed this into google, and the very first site that came up ( https://www.sciencelearn.org.nz/resources/47-colours-of-light ) disagrees with your list on yellow (600 nm). The second site that comes up ( https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/c/Color.htm ) has the same colour list, but different wavelength ranges: red 625-740 nm, orange 590-625 nm, yellow 565-590 nm, green 500-565 nm, cyan 485-500 nm, blue 440-485 nm, and violet 385-440 nm. In that case, cyan barely overlaps with your range, but they all at least overlap a tiny bit, although, I think that's not evidence that the issue is "cut and dried." HeNe lasers emit 632.8 nm, which everyone I know calls "red," yet, according to your list, is "orange" but according to the second list I found is "red." The third list that came up on google ( https://www.thoughtco.com/understand-the-visible-spectrum-608329 ) has limits that match neither your list nor the other two I found. Also, all four lists have different extreme limits and with the exception of google #2 and your list, don't even list the same names for every colour. I think that constitutes "open to interpretation" rather well.

Shouldn't diluted indigo dye have simply a desaturated indigo colour? Do other colours change their nature when diluted?

I googled and Wiki was the first to come up: https://en.wikipedia.org/wiki/Color Sorry, I can't keep up with the comments today, but I'll check back tomorrow.

Yes, pink is diluted red, right? But physics is different from art. In art pink is red mixed with white. But cotton fabric is already white. I gotta go.

Oh ok, so, basically the same thing as "midnight blue?"