Elvis Presley's BMW 507 Complete Restoration video

Hello guys. I just came across with this video and i thought that i would be great to share it. Fantastic car, with a nice history and a great work of craftsmanship on it. I didn't understand one thing though. Why they left some red part (untouched) on the left and right sides of the car, near the sills and front fenders, in the door hinge. I mean red it was not the original colour of this particular 507.

Link: https://www.youtube.com/watch?v=bh5Er5WrRKk