COLOR USUALLY CHANGES WITH TIME..
If your boat was new, or almost new, "codes" match would work (as on car paint).As already posted, however, some pigments fade faster than others and anything other that stark white or black is a mix of pigments, Another problem that can occur is that you get an initial color match and then the "new gelcoat" may have different make of pigmenets which fade faster, slower etc so that the repair eventually shows again. Another problem is that resins themselves do yellow somewhat.Of course. these problems can be largely prevented by proper matching, good materials (as from original euiment if possible), blending etc.I researched this extensively, and it is posted above (in the yellow area). Under Fiberglass and gelcoat Trilogy #2. Hope this is of some help.ThanksJim W