In the UK gel pens by Mitsubishi Pencil Co are half way there.
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apparently (flash junk) I just tried one. The bright pink one is good colour contrast and will write fine lines on black plastic. If you allow a day for it to dry then it is reasonably fast, you have to rub it firmly before the dried gel will rub off.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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