If doing a factory order, BMW will consider certain non-M3 standard paint selections, but typically it would from a palate of colors offered on other vehicles. The cost for US spec custom paint, if approved, is an additional $5,000.
You would likely be limited in matte colors though. Have you considered a matte wrap? From a previous thread, there is a shop in Germany that apparently will do a vinyl wrap (and probably others shops exist). With luck, someone else from Germany will chime in with the contact information from that thread.
2009 M3 E93 Silverstone II over Bamboo: 6MT, Tech, Premium, Cold, Premium Sound, Ipod, 19'' Wheels, OEM Exhaust Mod.