BMW, and probably every other manufacturer, uses an additive in their paint when used on flexible materials like plastic parts or flexible things like bumper covers. This allows it to flex a bit more than needed on rigid metal parts without breaking its bond to the underlying materials.
My i3 is over 5-years old now and I've not noticed anything unusual WRT the paint. It rarely gets parked inside, so it sees the full effects of weather from direct sun, snow, and rain.
A good sealant or wax is important for keeping the paint looking good. Luckily, where I park, bird poop isn't usually an issue. I do try to remove it when that does happen.
Black does show defects probably more than most other colors, though.
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above