good paint shops can analyse by tool the color and mix it very close to original. That def works on the silver.
Black parts are an issue, as per Doug. My research did show original "black" varys from plain mat paint to black with more or less metal i.e non mat paint. I ended up with mat paint.
I honestly don't think that the "factory" cared or gave much thought at all to the blacks that they used?
I think it depends more on when the car was built? A US GTS is not going to use the same flat black on the hood as say an 78 or 79 European car.
One is a true semi-gloss black and the other really a gloss black with metallic in it. Also the level of metallic seems to vary so perhaps that was a custom blend for each car built?
On a US GTS I'd just use "hot rod" semi-gloss on everything. No one is judging these cars with any authority to rate them for accuracy like the "Shelby's" are. So why worry about it?
Make it look good like there was a definite plan and not haphazardly eclectic.
Personally I'd just forget about the metallic black. You don't see that on US sold cars and that's the world that I live in.