Why are indigo and violet in the rainbow and not just purple?
I always learned “ROYGBIV” as the colors of the rainbow. Red, orange, yellow, blue, indigo, violet.
What’s up with the last two? Isn’t indigo basically just dark blue? Why is it violet and not purple? Can’t it just be “ROYGBP”?
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I'm confused...
Doesn't a rainbow contain all colours by definition?
It doesn't contain pink or brown. Some of the colours we see are how we register a mixture of light frequencies, whereas each point in the rainbow is just a single frequency.
What a phantastic thread!
We have had linguistics, sociology, physics and now biology in the form of colour perception so far.
Cross domain discussions are great! :-)
This is incredibly incorrect. While many colors that are additive are combinations, those combinations are simply approximations of the single wavelength true color. All colors are on a spectrum of hue, luminance (brightness) and intensity (saturation).
Pink is red with high luminance and high intensity, and brown is orange with low luminance and mid-high intensity
Nope. A whole bunch of colors do not correspond to any wavelength of light. This includes purple.
Among some of the colors that are not spectral colors are:
Grayscale (achromatic) colors, such as white, gray, and black. Any color obtained by mixing a gray-scale color and another color (either spectral or not), such as pink (a mixture of a reddish color and white), or brown (a mixture of orange and black or gray). Violet-red colors, which in color theory include line of purples colors (such as, approximately, magenta and rose), and other variations of purple and red. Impossible colors, which cannot be seen under normal viewing of light, such as over-saturated colors or colors that are seemingly brighter than white. Metallic colors which reflect light by effect.
https://en.wikipedia.org/wiki/Spectral_color#Extra-spectral_colors
Pink can also be described as a reddish hue with high brightness and low saturation. But saturation is a matter of how strongly one frequency is emphasized compared to other frequencies. So colors with low saturation contain mixtures of frequencies, but each point in the rainbow, when there's no other source of light present, is only a single frequency. This is why the rainbow doesn't contain any desaturated colors like pink. Brown, I admit, can be just dark orange.
Well yes, but the differentiation of colors varies by, believe it or not, culture! For example, the Japanese word for blue, 青 (ao) was used both (depending on context) for what we would call blue and green, and it wasn’t until modern times that a new word, 緑 (midori) started being used to explicitly define what we might call green. Even now, their ‘green’ traffic lights would be described as blue in other cultures. My apologies for the euro-centric over-simplification, but here’s a great article to elaborate further: https://cotoacademy.com/japanese-color-blue-green-aoi-midori-青い-みどり/
Interesting point.
And I am a little bit with the Japanese in this regard. At least my GF always complains that I am unable to correctly distinguish between green and blue ;-)
There's a difference between linguistic simplicity and color blindness.
Well in my case it's more about where to draw the line between blue and green.
I can differentiate the colours but just still call things blue that my GF (and most of the rest of the world, apart from Japanese and the german dialect I grew up with as it seems) already calls green.
This is a running joke in my house. My daughters like to wear a lot of blue/green shirts. Apparently I always guess it wrong.
Finally, I am not the only one! Feels good.
Purple, or violet, is a bit shorter than 400 nanometers regarding its wavelength.
https://pixfeeds.com/images/7/308404/1200-308404-483872671.jpg
Actually....
There is no purple light.
Kinda.
Video explaining it in detail: https://youtu.be/CoLQF3cfxv0
Several colors we can perceive only exist as a specific mixture of wavelengths. And purple (coincidentally for this thread) is one such - white light contains it, sure, but, you can't isolate it to a specific single band, like you can isolate cyan or yellow. So, no, rainbows can not have purple in them.
I disagree. That color he keeps talking about is magenta, there is no magenta light. I see purple in the rainbow, but not magenta.
You would be half correct. Magenta is impossible "in the real world". It obviously exists on your computer screen due to its ability to shoot colored light into your eyeballs
Well yeah. I guess my question should be “why do we learn indigo and violet when we learn about the rainbow”. It’s more cultural
Yes, exactly.
E.g. in Germany I don't have heard anyone using Indigo and Purpur as major colours but only in combination with blue : "Purpurblau" and "Indigoblau" describing certain forms of blue.
So only blue and violet in german rainbows. And ultraviolet because most of us are more engineer than poet nowadays ;-)
You'd think so but colours are weird. Some of the ones we see aren't ones that actually exist, they're invented by our brains. Magenta for example doesn't exist, there is no wavelength for it and because of the way our eyes detect light it should really be a shade of green. But our brain doesn't like that and invents a brand new colour instead.
