It's really hard to get the same perceived color out of a screen (which shines combinations of R, G, and B at your eyes) versus a physical thing (which reflects

It's really hard to get the same perceived color out of a screen (which shines combinations of R, G, and B at your eyes) versus a physical thing (which reflects a subset of the sun's radiation into your eyes). The way we do this only works for humans, incidentally. Most of the time, different things only appear to have the same color because they happen to map to the same "point" in color perception space, not because they actually produce the same light distribution.