First of all, I don’t understand why indigo and violet are split… why not just call it purple? Ok, not my question.
Colors of the rainbow all make sense to me except purple.
Red – orange – yellow…makes sense that orange is between red and yellow, and it’s the combination of those two primary colors, nice transition
This follows with green, blue. Green is between yellow and blue.
Now… if purple aka indigo and violet are a combination of blue and red, how can it be on the opposite end of red (very different frequency) and outside the frequency range of blue? I would expect a secondary color’s frequency to be between the two primary colors that create it
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Because light and colour are not the same thing.
Light is a form of electromagnetic energy with a wavelength between 400 and 700 nanometres
Colour is what our primitive monkey brains try and interpret as a ratio of red, green and blue.
Light is a spectrum of low energy to high energy. Radio waves to gamma waves. Visible light makes up a small portion of the light spectrum.
When you see a colour from a paint or a you’re seeing the colour that is reflected back at you as the molecules in the paint absorb all other colours apart from that one.
When you see a rainbow or a colour spectrum light, it is being split into its constituent parts based on how much they bend in the medium the light is travelling through. High energy light like blue and violet light bends more compared to low energy light like red light. This is why rainbows form.
White light, is actually a combination of all colors combined – all light at once, will create white light.
Light is actually waves, much like the waves at the ocean. Lets call the distance between each wave, the wavelength. This wavelength can be short, it can be long, and anything in between.
Our eyes, can not see all lightcolors. The longest wavelength of light we can see is actually red (the very start and top of the rainbow, which also is the longest arc this way). An example of lightcolor with longer waves would be infrared which is just above what we can see.
The shortest that we can see is purple, the shortest arc in the rainbow. An example of shorter would be ultraviolet, which is just below what we can see.
There’s a lot of answers here, but none that I’ve scrolled by so far seem to get to meat of the question (and a lot are definitely wrong to some degree).
The answer is that it’s a quirk in the way our eyes work. Light is composed of lots of frequencies and some of those are visible to us. Red is at the lower end, green is in the middle, blue is higher and violet is the highest we can see.
To actually see the light we have what are called cone cells (and rods, but rods aren’t really for color so ignore them). You have one set of cone cells that primarily see red, one that primarily see green, and one that primarily see blue. They don’t only perfectly respond to one frequency though, they’re activated by a range of frequencies and they have a bit of overlap. Yellow light for example is a frequency between red and green, and which triggers the red and green cone cells. So your brain knows it’s seeing yellow, as opposed to red or green, if both of the cone cells are activated. And so you can also trick your eye a bit by showing it a mixture of red and green light, which activates both of the cones and looks yellow to us even though it’s not.
Now, as for violet. Violet is above blue, so in theory it should only activate the blue cells, right? Wrong! For some weird reason our red cone cells also have a little bit of sensitivity to violet light. So if your blue cones are the only ones activated you see blue. But if your red and blue cones are activated you see violet. And so just like yellow, you can see a mix of red and blue light and your brain decides it sees violet/purple.
Indigo is different, it is the color between violet and blue. So it’s just a slightly different color, not another name for violet. The difference between violet and purple is usually that violet refers to the actual light in the spectrum above blue, and purple refers to a mix of red and blue that humans perceive similar to violet
In the Danish education system they merge indigo and violet. Probably happens in a few others
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Red has wavelength of 800 nm. Blue has wavelength of 400 nm. It happens that 400 nm light looks slightly red because it also activates the red pigment detectors, for whatever reason.
You can check human color cone response as function of wavelength here. [https://midimagic.sgc-hosting.com/huvision.htm](https://midimagic.sgc-hosting.com/huvision.htm) where you should notice that red cells have small hump at the extreme end of blue, so these colors being to look red again.
From a physical point of view, this is aberration and imperfection of our visual system. The spectrum should end with blue just fading out.
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