Hi aro03,
Aaron is correct, the Grey finish is the earlier head production which will have a 4mm bolt hole. When Matt released the E6/7 the head was updated with bushings to allow the use of 4mm Bolts for E6 Configuration and 5mm Bolts for E7 configuration.
All parts are identical aprat from the colour and the only part with any difference is the actual blade grips as these will have a larger hole in them to allow the fitting of a blade bolt bushing.
Hope this helps
Ross