Shouldn’t common sense dictate that either both be one, or both be the other?
In: 1934
When we stick purple (or violet) at the end of the rainbow, that’s not actually a good representation of wavelengths of light.
Purple does not fit in with the other colors, because there is not a purple wavelength of light. We only perceive purple when there is both red and blue light present. Pure frequencies can make red, green, yellow, blue, etc. But purple is a consequence of our brains interpreting the world around us.
This is why we represent colors with a color wheel, and frequencies with a straight continuum. The rainbow goes from red to blue, but our brains can blend red and blue together with a unique visual color.
No, common sense breaks down *really* fast with color. Color is *weird*.
https://en.wikipedia.org/wiki/Spectral_color and https://en.wikipedia.org/wiki/CIE_1931_color_space
https://en.wikipedia.org/wiki/Line_of_purples
https://en.wikipedia.org/wiki/Purple#Relationship_with_violet
Color arises from human visual perception, more biology than physics. The arc with numbers on the CIE diagram linked above represents the colors that are perceived in a pure wavelength. The eye has three types of color receptors that respond roughly to red, green, and blue. Kindergarten/traditional color theory uses red, yellow, and blue as primary colors for paints/pigments. Pigments are subtractive in that a red will absorb the other colors. Mixing the primary paints results in brown or black from absorbing everything. This is roughly how color printing works, but with cyan, magenta, yellow and sometimes black, or CMYK.
Light can also work additively. Shine red, green, and blue lights in the right ratio and you get white. Change those ratios and you can get a bunch of different colors and that’s how TVs and computer displays work, RGB.
Green and blue make cyan, red and green make yellow, blue and red make magenta (roughly), so CMY and RGB are complementary: https://en.wikipedia.org/wiki/Color_mixing Mixing red and green light gives yellow. Mixing red and green paint makes brown.
On the spectrum violet after blue.
Mixed red and blue is magenta.
[Magenta is an illusion](https://www.youtube.com/watch?v=DRuPF6JtWdw)
To make it very short. In light, red is a very long wavelength, actually the longest visible light wave. Purple is shorter as it’s a shade of blue, which is the shortest visible wavelength.
Mixing colors on paper doesn’t work by radiating light itself, but rather reflecting it using whatever light available around it.
I wanna give it a shot too:
Yes, magenta light doesn’t exist.
But! The way we see color is by using bits in our eyes that tell us how red, green, or blue something is, which the brain then mixes to get the other colors, for example, yellow is a bit green and a bit red, so if the green and red bits light up, the brain knows to mix those into yellow.
If something is throwing both red and blue at us, the red and blue parts will tell the brain so, and the brain doesn’t know that light that is “a bit blue and a bit red” cannot exist, so it mixes it into making magenta.
It’s actually sort of the same thing that causes both of them, in a sense.
Light and paint work differently. Paint works by absorbing some colours and leaving others. So red paint absorbs everything except red light, so we see red. Blue paint absorbs everything except blue light, so we see blue.
Light works in an additive sense. We have cone cells (light sensors) for red, green, and blue light. If we see a red light, the red cones fire. If we see a green light, the green ones fire. If we see yellow light, in between red and green, both fire a bit and we see yellow. However, if we see red and green light mixed together, we see yellow as well as we trick the brain by seeing a bit of red and a bit of green.
Purple is a funny one. If we see some red light and some blue light, our brain has to make up a colour. It can’t be between red and blue because that would be green except the green cones aren’t firing. So it invents purple.
Then we get purple paint. This is a mix of red and blue, meaning it absorbs some of the red light, some of the blue light, but all of the green light. I.e. the light that reaches our eyes is effectively *not green*, but has some red and some blue. So, we see purple.
The color wheel is a circle. The spectrum is a line. To fit the circle to a line, it has to cut somewhere. Purple is where that cut happens.
Purple isn’t on the spectrum, although violet is. Purple is a color your eyes see when both blue and red sensitive cones fire. The idea when mixing pigments is to have the unabsorbed wavelengths stimulate both the red and blue sensitive cones (and the best pigments for this are not necessarily red and blue).
Google ‘additive and subtractive color.’
Color/light works differently in different scenarios. Like a piece of paper is white until you ‘add’ color to it, a computer screen is black until you ‘subtract’ color from it.
Ok. It’s important to separate two different colours here:
1. There is violet. Violet is at the very edge of the visible specturm, which is why wavelengths beyond violet are called ultraviolet light (UV).
2. Then there is purple and magenta. This isn’t a real colour. it’s a colour that’s created in your brain. That’s because the eye has three different cells that see light, so called “cone” cells. We have one type that responds to Short wavelengths (Short/blue, with a peak response near violet-blue), one for Medium wavelengths (Medium/”green”, with a peak response at Greenish-yellow) and one that sees Long wavelengths (Long/”red”, peak response at Yellowish-red). Depending on how strong the response is from each type of cells you see different colours. You see purple when Blue and Red cones are triggered, but not Green (ie, a mix of light from the blue and red spectrum).
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