I wouldn’t even say that the supernumary bands are particularly rare. When I was living in Montana, they seemed to show up in about half of the rainbows I saw (which was a fair number of them). Though this might ultimately just be a statement about the climate in Montana, that for whatever reason it’s unusually apt to produce the conditions for supernumary bands (just as they also seemed unusually conducive to producing rainbows in the first place).
Utah, where I lived for a few years, was great for making rainbows – the Wasatch mountains provided the conditions for clouds to dump rain, especially after having picked it up from the Great Salt Lake. If the sun was getting close to sunset at the time, the angle would be perfect for a rainbow. And with the mountains behind the bow, it’d be particularly visible. (And if the sun was very close to sunset, you’d get an orange-and-red Rainbow Sunset, since there was little green or blue present to b scattered.) and I do think that I saw more supernumeraries there than elsewhere. But it definitely wasn’t even close to half the rainbows I saw.
Great info on the supernumary bands! I’ve seen them before and have wondered why there were sometimes extra bands in some rainbows (although apparently I didn’t wonder enough to actually research it.)
From Wiki:
Later scientists conclude that Newton named the colors differently from current usage.[20][21] According to Gary Waldman, “A careful reading of Newton’s work indicates that the color he called indigo, we would normally call blue; his blue is then what we would name blue-green, cyan or light blue.”[22] If this is true, Newton’s seven spectral colors would have been:
Red: Orange: Yellow: Green: Blue: Indigo: Violet:
There’s no “if” about it. On those pages where he doesn’t write about five colors (representing his older, pre-octave thinking), Newton in his Optics lists these seven colors, in this order.
And it’s not too hard to reconstruct what each color was he was referring to, since he gives their characteristic lengths.
Ah, so his “blue” is indeed our cyan/sky blue, and “indigo” is our “blue.” That makes a lot more sense to me if I were forced to divide the rainbow into seven colors.
Right-- Roy G. Biv.
But nobody is disputing the names of the colors. I’m curious as to what names the colors refererred to in modern English usage. It seems to me that ROY G. BIV is really what today would be ROY G. CBV or something like that.
Here’s where the Wiki cite comes from with a graphic representing the colors today. “Blue” is a sky blue and “Indigo” is a deep blue. Kind of reminds me of the distinction in Russian between sky blue and deep blue, where they have individual words for the concept, rather than relying on an adjective to modify a base color name (“blue.”)
Pythagoras named the colors: white, black, red, and yellow
Aristotle added blue, green, and purple
Newton did not subscribe to the earlier Emission theory and as earlier writers like Ptolemy had written about refraction white and black were dropped as colors.
Orange wasn’t a named distinct color until orange trees arrived in Europe after the 15th century.
As color perception is a human trait and not a physical trait “roy g biv” is merely a social construct. There are some claims that Newtons seven colors could relate to Pythagoras’ theory of music but I can’t find any reliable historical documents to support this claim.
If someone has hard evidence that purple vs. indigo was based on anything more than cultural differences it would be appreciated.
In Japan, they did not differentiate the color green until recently.
Green was considered a shade of blue and in many ways still is in Japanese language (for example a green traffic light is given the same name as their name for blue). Even the concept of green as a shade of blue didn’t come about until the Heian period (roughly 800-1200 CE) and calling them distinct colors only began after World War II with the American occupation.
I could actually see that. Depending on the traffic light and the type of lights being used, I find that what we call a “green” traffic like is closer to aqua blue. But it does vary a bit. And “yellow” is, to me, often closer to orange than it is yellow. (Calling it “amber” is actually most accurate to me, if choosing between “yellow,” “amber,” and “orange.” And many places do call it “amber.”)
Purple is Murex and indigo is Indigofera tinctoria. At least, that is what they are based on.
Azure versus cerulean versus cyan versus blue versus Japanese versus Russian colors, I’ll let someone else fill in the details.
If one word was used for green and blue, why not translate it (at least before the 2nd word arose) as green? 
Some linguists have observed the following:
All languages have at least 2 colors - white and black
Languages with 3+ colors have red.
Languages with 4+ have green or yellow
Languages with 5+ have green and yellow
Languages with 6+ have blue
Languages with 7+ have brown
Languages with 11+ have purple, pink, orange, gray.
I observe something like this in Thai. While they do have simple words for all eleven of these colors, in rural vernacular “lazy” approximations are often used: ‘Red’ for brown, and ‘Green’ for blue! (For example, a woman with dark brown hair is said to have ‘red hair’, less surprising than at first glance since most Thais’ hair color is naturally jet black.)
I suppose until the Heian period and “midori” you could have, but once that occurred you could see which word represented which color.
I guess it’s like, why do we call “pink” its own color when it’s just a light shade of red?
Actually, a lot of “pink” turns out not to be simply light red, but actually light purple – it can’t be represented by a single spectral line. You have to mix two spectral colors – blue and red - in order to get the actual shade. Surprised me when I found out, because I, too, used to think that pink was simply “light red”.
I don’t think “cyan” is actually what Newton intended. The Cyan stripe on a seven-color rainbow flag looks horribly out-of-place.
That is, or rather more of a sky blue, the color that is shown in the Wikipedia cite you mentioned, though.
Like in this version of the rainbow flag.
Maybe cyan is not quite the name for that light blue, but it’s close enough. And I see it in other depictions of the rainbow.
Note the “calico craze” which lead to the rise of indigo dyed fabrics from India during Newtons time wasn’t just used for the “dark indigo” that Newton used in his “Opticks” but also for all shades of blue, and some greens and purples.
Apparently several countries implemented protections policies because the fad was impacting their local textile industries.
I am pretty sure that Newton used “indigo” due to that social fad vs using the word “purple”.
I would bet that artists caused some drift from the names he was using.
http://www.gutenberg.org/files/33504/33504-h/33504-h.htm
It appears that the Indian fabric fad is known to have increased the number of French words for different shades of blue so I would expect the same happened in England.
We can actually answer the question of what color Newton was naming “indigo” by using his own scheme of equating the musical notes with the characteristic lengths associated with the colors – which we now know to be wavelengths. I ran the calculations, and found that Blue came out to be about 465 nm, indigo about 417, and Violet about 390. By comparison, Wikipedia and other sources give about 470 nm for blue, 450 for Indigo, and 420 for Violet.
You get slightly different values if, instead of the “Classical” values you use even tempering of your scale, but not that different – 488 for Blue, 450 for Indigo, and 387 for Violet. You can look these up on a spectrum (although if you look at an on-line source, you won’t really get proper color reproduction).
This is from a piece I wrote titled “The Well-Tempered Spectrometer”, which hasn’t yet been published.
If, instead of a simple octave, you go with a Chromatic Scale (which includes the “black keys” on the piano), you’ll end up with a new color at 690 nm between Red and Orange, one aty 615 nm between Orange and Yellow, one at 516 between Green and Blue, one at 460 between Blue and Indigo, and one at 410 nm between Indigo and Violet.
Imagine that you’re a modern-day Newton trying to buttonhole your friends into seeing these new colors, and come up with names for them.