Bringing my years of Aerospace wiring experience to the auto world, I am building a pair of Harnesses for one of the Singer cars this week. Specifically it is a Engine harness so there is something on the order of 100 connections to all the various components each of which get their own distinct wire color. The task is very time consuming and involved since making even a single mistake can cause pretty big problems. I will post more pictures as the harness starts to take shape.
Each wire color carries its own function, of course you could stick to using a few primary colors, but using colored/stripped wire saves much time when it comes to assembly and troubleshooting in the future.