I think I read somewhere its actually a lacquer? So it's just applied on top of of black and silver mix of paint. You could just look on the bmw forums. I was looking at this stuff for a bit but realized it is just about the most expensive paint/lacquer? you can get. I'm still not completely sure on this but look on the bmw forums and you will probably find something.
jut found a link saying it was a lacquer
BMW Shadow Chrome paint 5Liters - Bimmerforums - The Ultimate BMW Forum