This was a good explanation - they simplify at points, but make it obvious they're doing so, which I'm fine with. I would have liked to hear more about how the

This was a good explanation - they simplify at points, but make it obvious they're doing so, which I'm fine with. I would have liked to hear more about how the artists' color wheel came to be. It's a model, after all, and models don't have to be true as long as they're useful. The RYB color wheel is definitely not useful for setting colors in CSS, but as far as I know, the story goes something like this: Before today's industrial processes, the colors of paint you could make or buy were those one could make from natural ingredients, for example cobalt for blue if I remember correctly. Artists and their suppliers noticed that if you had red, yellow and blue paint, all of which one could make from the materials available, then you could mix them to make any color you wanted (possibly with some white or black added to lighten/darken, or tint/shade if you're being pedantic). Further, you could make a lot of colors by mixing at most two of these colors, and it was purely the proportions of the mix that mattered, not the raw amounts. So these got called "primary" colors, and it was natural to represent them in some way - to the engineer, a triangle seems like an obvious choice where the mix with 25% red and 75% blue lies 0.25 along the line from red to blue. Artists chose a circle instead, which is really the same model (mathematicians would say it's a topologically continous deformation from one to the other). At the time, the color wheel model turned out to be useful, and so it stuck around and got taught in art schools. Magenta, Cyan and Yellow would have done just as well as starting points, but were harder if not impossible to get from the natural materials used at the time. On the other hand, orange or brown as a starting color would not have got you the same mixing abilities as far as I'm aware. Brown is an interesting data point on its own because you can make it by taking orange and shading with a small amount of black, but you can also make it by taking orange and adding some blue (among many other ways), so now you're using all three primaries and fall off the color wheel. And that's before we talk about perceptual brightness and gamma correction and all that. Red, Green and Blue on the other hand is a useful starting point for things that emit rather than absorb light (with similar but different caveats).