I have a hand held spectrophotometer that gives me color formulas to match vinyl, leather, Ultraleather, and plastic. Once in a while it gives me a formula that is right on the money, but most of the time, I have to play with it to get it just right. It's a good starting point, but it's not dead on. I'm sure that will be the case in matching paint too.
No one lives forever, the trick is creating something that will.