this was done on the factory cars at the 86H Nurburgring race (Marathon de la route)
3 cars were raced, which were all orange
so the bumpers were painted like this (except each car had a different color) to easily recognise them

Back in the sixties Porsche painted ther racing cars white and would add accents in different colors to distinguish the various cars when they had multiple entries. Ferrari and Alfa Romeo also did this. Actually this is still done today by teams with multiple entries. Audi paints all of its cars (R8 and R10) silver and uses different accent colors for each car. The Dyson does it with their Lolas. Penske, Gannassi, and Rahal do it with their IRL cars.

I see - cool! Just running through different colour schemes for my car when it comes to paint

And Porsche painted all the cool race car Orange cuz its the best color!

I was thinking white at first but orange is growing on me.... I'll post pictures of the project when the donors arrive at my workshop

Up until 1970 "most" factory race cars were white. But that seems to have ended in 1970.

I'm basically repeating what everyone above has already said.
but I wanted to add that a tiny part of the reasoning for having the different colors as identifiers, was due to the lack of in car radio's and communication.

so the pit crew had to be prepaired and recognize whom was coming in without being able to listen to it on the radio.

my car:

When they look down that long pit row and see a 914 coming down it, they will know which one it is. Hard to see the numbers from the front.

It all makes sense now - just wish I had 3 to make it worthwhile