Growing up, I was taught that rainbows have 6 colors. Red, orange, yellow, green, blue, and purple. It makes sense as it goes from primary color (red) to secondary color (orange) back to primary (yellow) back to secondary (green), to primary (blue) and finally ending on secondary (purple). Indigo is a blend of blue and purple, but purple is a blend of red and blue…..
In: Physics
I read somewhere that Newton wanted there to be seven colours because that’s a lucky number. Of course rainbows are a full spectrum so have as many colours/shades as you want
The words we use to describe colors are arbitrary. Indigo is a word used to describe darker shades of blue.
There is some evidence that ability to discriminate different colors depends on the number of words for different languages–different cultures depict them slightly differently and teach numbers of colors differently. In American classrooms they’re typically taught as seven colors (Red, Orange, Yellow, Green, Blue, Indigo, Violet).
That doesn’t really answer your question, though. The electromagnetic spectrum and the color wheel are separate things. If you mix red and blue paint you get purple, but that is not a simple physical relationship.
Colors as we perceive them are a function of the wavelength of the photons (ranging from around 400-800nm roughly). The colors we perceive essentially band these wavelengths together into a color we describe with a word (ranging from violet at the lower wavelengths to red at the higher ones in the opposite order I mentioned earlier). Primary colors are arbitrarily selected–Red, Blue, and Yellow are one set of primary colors, but so are Cyan, Magenta, and Yellow.
When we describe a rainbow using named colors that’s a simplification. A real rainbow isn’t a strip of red and then a strip of orange and the a strip of yellow. It’s a continuous spectrum of light that blends gradually from one color to the next.
A rainbow you draw using crayons is like a set of steps, each one is unique and you can count them.
A real rainbow is more like a ramp. There’s no individual steps, you can’t count anything because it just gradually changes height from the bottom to the top.
BTW, the “primary” and “secondary” colors you listed are only one system of colors, specifically used for pigments. For light emitting devices like cell phone screens the primary colors are red, blue, and green. To make yellow you combine red and green light.
Fundamentally, what we call the colors of the rainbow are somewhat arbitrary. The rainbow contains a continuum of colors, so there’s theoretically infinitely many of them. We just like to group these into finite categories because our brains handle that better than infinite continuums.
Isaac Newton, in particular, categorized the colors of the rainbow into seven groups: red, orange, yellow, green, blue, indigo, purple. He did this because he thought seven was a magic number (seven days in the week, seven planets in the sky, seven notes in a major scale, etc.) And he was reaching to make this work, including the then-obscure colors of orange and indigo to bring the accepted five up to seven. And this Newtonian naming system has stuck around in public conscience despite not being that useful for color theory, which is where we get the idea of primary and secondary colors.
Given what we know now about human color perception, it would probably make more sense to use a six color system: red, yellow, green, cyan, blue, magenta. The three colors of light our individual cone cells are most sensitive to, and their opposites. Which ones are primary or secondary depends on whether we’re printing with ink or rendering with light.
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It’s just names for colors. The way I learned it in school was to remember Roy G Biv.
Red, orange, yellow, green, blue, indigo, violet.
Isaac Newton believed that the universe is mathematically perfect, and that things come in sevens: 7 notes in a musical scale, 7 days of the week, 7 objects in the solar system, 7 colors in the rainbow. I’ve heard different explanations for why indigo specifically, including that it relates to trade/commerce. Regardless, indigo is not a distinct color the way blue or purple is, and it probably doesn’t make sense to include it in the “official” colors.
> primary color (red) to secondary color (orange) back to primary (yellow) back to secondary (green), to primary (blue) and finally ending on secondary (purple)
That’s the wrong structure of colors often taught in schools and other places. Depending on your view the primary colors are either red, green, blue (additive mixing) or magenta, yellow, cyan (subtractive mixing). Yellow is an additive mixture of green and red, which is what your monitor does.
English is full of fishy lists of seven of things because seven was a Christian number and people loved there being seven continents/colors/seas etc in ways that really don’t make much sense
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