Here's a tip I use for larger scale stuff...
I get telephone wire...the 4 conductor type with the solid wire core....I take the yellow and black wires and cut them into small sections, and using a pair of tweezers and a piece of brass wire, I push the little piece of copper out of the middle. I then re-thread them onto a piece of brass wire and touch them with superglue. The result is a perfect demarcation line between the colors. I do this with arrestor hooks (when applicable) using larger wire. Once it's dullcoted you can't tell the difference.
I'm pretty sure you can find wire with colored jackets that would be small enough to use with 48th scale...
Jeff