Comment by jcranmer
4 hours ago
Yes, people use it in practice. But it's not being used for the thing you're thinking of.
RGB is fine for specifying a color. I mean, there are issues with RGB colorspaces and whatnot, but if you need to pick the background of a page or the color of text, there's no real reason not to use RGB.
The problem with RGB is that it is really bad at color interpolation. You can't take the average of the red, green, and blue components of two colors and expect a usable color in the middle to come out. Instead, you need to move to a perceptual color space. CIELAB is the old perceptual color space of choice; Oklab is the new perceptual color space of choice.
Color interpolation is needed for things like gradients or information visualization, where you need to say things like "20% of the way between color A and color B".
RGB is also highly unintuitive by itself. Because additive color mixing is unintuitive. There is no way of knowing what RGB mixture corresponds to yellow unless you have memorized it.