had a rear bumper replaced on silver GD, didn't match exactly, but then again original paint had been exposed to British weather for 5 years and bumper had never seen daylight before. Not surprised they don't match exactly, but pre-painted bumpers are one of the things that car makers do to keep insurance cost down, if it wasn't painted it would cost almost twice as much to replace and still no guarantee of a good match (seen some shocking paint jobs). Painting on plastic parts was always problematic as special undercoats and prep needed to get paint to stick to polypropylene mouldings.
metallic paints are notoriously hard to match, the temperature and humidity when they are applied can change the look of the paint.
