I was working on my modified car and found I had too many white wires in the harness. I have a shrink tube marking machine (think of white shrink tube but with typed on writing) but the wire is still white.
I wanted a colored stripe on it. I looked at how others had applied stripes to heater hoses and it germinated this idea.
I found a piece of tubing that had a slightly larger ID than the wire. In this case brake tubing.
I drilled a small hole in the side so that a marker tip would fit into the hole. Vary the hole size for stripe width. Debur the ends and the hole. I used a small awl.
I ran the wire such that it came out of the tube closest to the side hole.
Press the marker down and pull the wire. It might work best if someone pulls while you handle the wire and the pen.
This process applies to those of you who have a light colored replacement wire, but want to make it look more production. Replace the permanent marker with a paint pen? Experiment!