I don't know if anyone else found this, but I found that some cars have discolored parts, these parts have the same color shade as the car's base color (eg. If the car is red, the discolored part will be a darker red.)
Cars that have this problems (those that I found)
Audi A2 1.4 '02 (plastic parts around the car, grill, the chrome trim on the boot hatch.)
Chrysler PT Cruiser '00 (Rear bumper)
Citroën Xsara VTR '03 (Fog lights, grille, front and rear logos.)
Fiat Panda Super i.e. '90 (Front bumper, mirrors, ventilation ports.)
Opel Tigra 1.6i '99 (Rear bumper skidpad)
Vauxhall Tigra 1.6i '99 (Rear bumper skidpad)
Renault Mégane 2.0 IDE Coupé '00 (Fog lights)
Renault Mégane 2.0 16V '03 (Door handles, silver element under the side turning lights)
TVR V8S '91 (fuel cap)
Alfa Romeo 156 2.5 V6 24V '98 (Door handles) (found by
@CSMDuty11)
This can be fixed by repainting the car.
Before:
After:
Before:
After: