The white teflon wire is excellent for aircraft because it does not melt
easily or burn.

Although they sell marking numbers and a kit, a simple way is to use the
small heat shrink tubing slightly larger than the teflon wire for marking.
With a few different color heat shrink, you can identify each end of the
wire with unique bands.

And, if you want to put a bit more work into it, you could use the standard
color code bands to identify pin numbers on plugs. For example, a brown and
red band would be pin 12.

This requires some standardization to make sure you are not upside down, or
you could always use a different width to start.

Prices varies a great deal on heat shrink tubing, do do not get ripped off.
I find it is handy to have a number of different sizes and colors. Clear
heat shrink is good for labeling, as Jim mentioned.

Colin