I would stick with Chrome. I think Chrome complements blue better than black. However I have not seen in person - my opinion is based on previous BMWs I have seen. I prefer black accents on light colored cars like White and Silver, as well as Space Gray which is not light but needs some contrast to make the accents more visible. The trouble with black on MCB is it reduces contrast between the accents and the car. Since the whole point of an accent is to be visible it diminishes the point of having an accent. You may as well go body color with the grilles and debadge.
Also I think you need to black the exhaust if you are going to black the grilles and badges. Although if you go down that path you could order Cyba's Carbon slip on tips.
2014 ///M5 Individual Frozen Grey, Silverstone Full Merino, Piano Black, Exec Pkg, Drivers assistance plus, LED Pkg, Bang and Olufsen, 343M