[ithacaartist]

But wait! There is yet another option. I have some stuff called "dial wax" in the form of a small, round white cake. It is designed to be rubbed into recesses to make them stand out, e.g. using it on the "on" and "off" buttons of a motor controller switch results in high contrast letters on black and red plastic. Wipe off the excess with a soft cloth.
Similar to this would be an all-surface marking pencil by Stabilo, or even a white china marker, both of which would allow excess to be removed by soft cloth.