Most auto paint colors in the last few decades have 5 to 9 toner components in their makeup. Metallic and pearl colors are especially tricky to mix by eye. Most of the time we start with something in the ballpark and then add or subtract toners to fine-tune it for a match. You only know if it looks good when it is sprayed out (with clear if required) and dried. All colors change in the spraying and drying process. I have spent hours and $$$ in materials trying to nail a difficult color.
The good news is that gas pumps in the old days used simpler colors with no metallics, etc. Mixing or modifying those to get a match is much easier. Still takes a skilled, experienced eye to do it. Computer scanners or color book chips get you in the ballpark, then you adjust with toners to match.
But what do you match? An old chip from a color standard that may or may not be correct? Matching a tangible item that is going to be on or near the restored pump is a fairly sure thing for satisfaction in the end.
