Ask around for a reputable shop that has a paint camera. That's likely not the correct name but what I'm referring to is a device that photographs the existing paint and mixes custom to match exactly.

Just had it done on my E39, the new spray and the original 14 year old metallic blue were dead on. SmileWavy

The only way to match this is to mix up a batch of paint (I'd suggest having the shop that will paint it also mix the paint) and spray it on a test panel (metal, primed with whatever primer you are going to use). You'll want the guy shooting the tail to be the one shooting the test panel. Once it is dry, look at it in several kinds of light. Direct sun, shade, etc. If it matches, proceed with painting. If not, proceed with changing the mix and do it again. You might find it matches in one lighting condition, and not others, so you have to pick your poison.

It might be helpful to find out what paint is on the car and use that same product.

I use a local shop that matches by eye with an endless supply of chips, then mixes their own paint.

JR

Spot on JR.. pretty much what I said in post #12.