well- I wasnt even born when these cars were racing around in Europe- and someone may be willing to correct me if I am wrong- but they are called pit stripes or team stripes- so that when a car was either circling the track or coming into the pits they could differentiate the cars- as they had really similar colors- This allowed the correct team to work on the car when it came in to pit-
a modern version of this same idea can be seen on the Porsche GT1 cars with their red and yellow fender mirrors and nose paint-.
or the Audi R8's that run at LeMans, they run a yellow car and a red one- and last year a red and black one. So that they can be easily disdinguished from afar.
I know their models but you get the point
The Gulf GT40s had three different variations on the classic blue and orange paint. I wont post the pics- you can do a search on google or something else if you really want.