Just to add another thought to this -
for any given input device, it is not certain that all possible RGB
values extrapolate to real colors. It is quite
possible (and happens regularly with things like cameras) that
extrapolated RGB values wwill map to imaginary colors (i.e.
-ve luminance, or chromaticities beyond the spectrum locus).
This is for two reasons, one being that the RGB ranges are
arbitrary in relation to the corresponding real world colors,
and an input device typically is a different observer, and
so doesn't "see" color the same way as a standard observer.