I can't find the source, but I remember reading that they actually found an M5 in that color to serve as the hero car. They only came in black in NA, but they have many colors for the worldwide release:
https://bimmertips.com/bmw-e28-m5-oe...color-options/
Obviously, they mocked up some non M cars to look like the M5 to save some money for the stunt cars.