Depending on the model ( triple black etc) it'll either be M957 Magnesium or M 963 Granite Grey. All of this info is available at MAX BMW website along with part numbers etc. Alan
For the darker grey Granite Grey is a good match, though not good enough to just touch up a few scars. I found that rattle can paints would stand the temperature but weren’t very tough. And I did manage to damage a few valve covers in my time. Mine was a Rallye with the darker grey colour.