This is accurate, but even “magenta doesn’t exist on the color spectrum” is misleading.

Human color perception doesn’t exist along a spectrum. It’s a 3D space. And if you collapse down the brightness dimension or take a cross section, it looks like this. The spectrum of monochromatic visible light is the black curve along the outside, which means that pure monochromatic light is an infinitesimally small line along the higher dimensional space that is perceptible color. The majority of light we see is not monochromatic, even if we loosen up the definition to mean “pretty close to monochromatic”. So while you could say “most colors don’t exist”, I think it’s more descriptive to say that light frequencies don’t have a color at all and that color is a purely perceptual phenomenon. I can explain this more if anyone is interested. It has to do with the 4 psychological primary colors, color opposition axes, and the way our cones simulate the behavior of a Fourier transform.