X2 on these guys. They have everything you'd ever need.

 

I just ordered this stuff it seems easy and fool proof hope it works. https://www.drcolorchip.com/

 

Just remember that the stuff you buy may be perfectly matched to a NEW paint job, but with fading from the sun may show up as a slightly darker color. you can feather it in to try to match a little better if you have severe fading. If it is just for rust protection then it won't matter