Whatever color you go with my advice is to have them powdercoated vs. painted. I am not sure how much you track the car (if any) but I have seen you post a few events that you attended and it seems like you might be the type of guy that puts the car through proper usage.
As you know I painted mine and my brakes got too hot on a track weekend and it roasted the paint. I just had mine redone and went with powdercoat this time.
Prismatic has the best color selection:
http://www.prismaticpowders.com/powder-coating-colors/
You will want color powder and also clear powder. I ordered 10lbs of each and it was WAY too much so you are probably fine with 5lb color and 5lb clear. I went with Prismatic because the local powder coating shop doesn't have a huge selection of colors -- your shop might have what you need though.
If you are going to go with the BREMBO decal (or even the M decal) you will want to apply the decal after the powder coating has been done. Then you will want to take the calipers to an automotive/body shop and have them clear coat ONLY the flat face of the caliper where the decal has been applied (just to seal the decal on the caliper). Don't have them clear the entire caliper because (again) paint and heat don't play nice.
You can get the BREMBO calipers made by this guy:
http://www.ebay.com/usr/advantage-design
He makes quality decals and he ships them quickly. I went with a 5" width on the newly done calipers I just got back from being powder coated. 5" is probably the max you can go otherwise it's going to look funky.
Also, if you are going to have them powdercoated you need to make sure all the seals are removed (or the oven will roast the seals). I suggest you have BMW break down your calipers for one reason. I've had BMW break down my calipers twice and on both occasions a bleed screw broke off. On the first occasion BMW warrantied it out (no charge) but on the 2nd occasion BMW would only cover 2/3 of warranty cost. The other 1/3 was covered out of pocket by my local BMW dealer due to me being a good customer I guess.
Sorry for the lengthy post... I kind of went through hell and back with my calipers from being painted to being powder coated. Would hate to see you go through the same so hope I can help with the information provided.
Brian