Different paint after painting bumper

Hello, I have a short question about the painting of my bumper and I hope you can help me. I recently had the bumper of my Alfa Giulietta repainted. The background was that I was disturbed by the pre-assembled plastic holder for the license plate, because I use a short mark and never really fitted it to the holder. When I picked up the car from the paintmaker (free workshop), I noticed that the bumper shimmers in the light somehow differently (pictures included). In my opinion, the paint was not hit properly. The paintmaker has a very good reputation and many years of experience. He used original Alfa paint and allegedly also took a sample from the door before to adjust the paint. After I brought the car back, he tells me that it is not possible to achieve a better result with this shade and that it is due to the difference Kunsstoff/Metal as well as to the grey tone. What do you think? The difference is especially noticeable from the side, frontal it goes.