It is not an exact science. And like others said, don’t assume just because the color says it is, that it matches. The color on the bottom is TruColor YN3 Yellow, which is too brown. But ART reefer yellow turned out to be a pretty good ringer. Same went for the blue. The right color turned out to be Amtrak Phase V blue, not CSX blue.
A body shop supply store should be able to mix you up a spray can of paint for plastic. If you can find one, you may have some success.