The problem you will have is what was the car painted with? How do you know that the color on the car is "right" on. There are a lot of variables when painting a car, IE color mix of the paint, air pressure (PSI) it was sprayed at, relative humidity at time of paint application, etc...metallic colors (especially FC7, EB3, EB5) are very variable, but even solid colors can be a little different.
Best bet to matching an existing paint job is to either get a computer match deal, they have a tool that samples your paint, then matches it. Or start with the factory Sublime, shoot a test piece, then tint and reshoot until you get a perfect match. If you were shooting an entire panel, say a door or fender, best bet would be to do all of the above, then blend it into the adjoining panels. Since we are only talking about a mirror, i'd say do the computer match deal, a lot of paint shops have that system.