I'd recommend using an HVLP gravity gun. Overspray is less prominent with this type of hardware. Covering the surrounding areas with a piece of plastic sheeting is also a nice touch.
One thing to remember, color matching is difficult. On an interior you have plenty of flexibility as the surfaces do not see much light and there are many breaks in the panels where you can stop spraying color.
Factory published color formulas always come with a "variance" set of shades for each color code. So if you have a GM color code 1SM, there may be 4 variences associated with this pending when the car was manufactured.
Not that this is a big issue with interiors, on exteriors its an art if you can master it.