In thinking about the locomotive wiring, almost all of the wires are gray - everywhere. All of the wiring harnesses are gray wire. with a few heavier blue wires. I don't recall seeing but 3 colors depending on the gauge wire. Gray, blue and dark gray. The only places that I can recall where there are colors like red, white, etc in on the gauges mounted in the control stand. GM bought the gauges. So what makes me such an expert? Many moons ago I worked at Electromotive in La Grange/McCook IL. I was a Locomotive Electrician. During my time there I worked assembling and wiring the main control panel, (a 4ft x 6ft panel) control stands, and then finally worked at locomotive test. Test was where all the wiring errors, defective parts, etc. were sorted out. I even worked on an all electric prototype locomotive for Europe. It was a high speed all electric unit that was very futuristic looking even in today's standards.
The only thing I regret was not getting exterior dimensional blueprints of the various locomotives that GM made over the years. It would have been a nice collection to hang on the wall. GM frowned on that activity. Many of the rules were still on the books from the WWII days when Nazi spies and sabotage was a very real concern.
There was one woman that worked there since WWII as a welder. She was a hoot to talk to.