My local motor factor mix their own, I've had mixed results from them. My VW colour was spot on, but I got some BMW 'grey' for my wheels, which was nearly black, and the intense blue for my Note (See my pics of the headlight masks) is almost right, but to me, almost sticks out a mile!
each colour code esp met/pearl/mica colours you get 5-6 met/pearl/mica variations then anything upto 15 shade variations, a decent paint shop will have paint chips so you can match the paint, failing that thay should have a paint analyzer take a bit of trim in and thay will match it
I use to do custom airbrushing (only do it for myself now tho)
i have 3 shades of bv4 (intense blue) one is dark and 1 is bright blue with very little metallic, the 3rd is just right