I know in the world of miniatures (especially military models and figures) that correct colour matches are thought to be extremely important as well. But don't they also take into account the effect of a model's scale (thus size relative to the viewer)? Doesn't this mean that the "correct" shade for the prototype (if there is such a thing) will be different depending on what scale you model in as well? (Not to mention the lighting, etc...)
Yes, they are important, usually you use the same shade a couple of steps brighter if possible to punch up the figures and models a bit. As others have pointed out, if you use straight prototype colors they will look awful. What's really important is that the relative hues be roughly correct, this is where a defined reference like the printing industry uses would be cool. Take the color and go up a few values, and viola you have a reasonable match in scale for your color. Since my cars range from ratty to just built, it would be nice to have colors that are close for the newly built cars! So if anyone picks up some Pantone or equivalent numbers, please post!