I don't think the 3rd metaphor fits. rgb values still points to a single color, which maps back to a single value on a 0 -> 1 or red -> violet continuum. It's more apt to describe it like a multi channel audio mixer. Many different channels ("really into a specific topic", "freaks out at parties"), each with their own value (10%, 20%).

Metaphors often fail though, so it might just be best to say what we mean plainly.

> rgb values still points to a single color, which maps back to a single value on a 0 -> 1 or red -> violet continuum.

No, it doesn't. Wavelength is unidimensional, but color can mix many wavelengths, and RGB is a 3d color system which doesn't cover all combinations of visible light but does approximate the way most human vision works, and is therefore useful as a description for human-perceived colors (and more accurate than picking a single point on the unidimensional wavelength spectrum for that purpose.)

An RGB value points to a single color, but if R is "really into trains" and B is "repetitive behavior" and G is "susceptibility to sensory overload", then it's basically the same metaphor as a multi channel audio mixer, except understandable to a different (and likely bigger) pool of people.

RGB doesn't map to a single line, you're thinking just about the hue. RGB is a proper vector that addresses a whole 3D color space.