The same thing happened with my old Venza when the rear bumper had to be replaced after a collision. The bumper definitely looked like a different shade of grey than the rear fender. When I complained, they re-painted it and they were able to match it a lot closer. There were several reasons/complications they mentioned with plastic bumpers, which I think are true for all cars:
- Even in the factory, the plastic parts are generally painted separate from the rest of the body, so some variation can be introduced there
- The paint that they use on the bumpers has to have a flex additive (so it won’t crack if something bends the bumper), so you’re already dealing with slightly differently formulated paint
- Metallic or pearl paints are notoriously difficult to match
- More specific to bumper replacements, body shops generally do not blend bumpers. They’ll blend when they replace fenders or doors to make the paint appear to match, but not bumpers.
Granted, most of the above applies to replacing a bumper, not getting the car from the factory with an obvious mismatch like the one in the OP’s photo.