It WILL match if they have it painted by a BMW-certified painter, and he uses "spray-out" sheets to get the exact paint match. Bumpers are attached to the cars in a separate facility after they roll off the production line, and they're just slightly different shade than the car body.
True story - had an aero lip painted and installed on my 07 E92, and watched painter match his sprayouts against the bumper and the car body - different shades. If they match the sprayouts to the car body, the painted bumper will actually match the body better than from the factory.
2013 F30 335i M-Sport 8AT/MPE/MPPK, 2011 128i M-sport Cabrio 6MT/PE