I just discovered that you can use a coloured pencil / pencil crayon on a painted miniature. Thanks to a friend of mine who told me about it. Maybe old news to you, but I would never have thought of using coloured pencils on miniatures.
I borrowed my wife's Prismacolor Premier White and drew lines on a Philippine Insurgent 28mm Tiger Miniature. I had painted some blue Rayadillo uniforms, but without lines. I popped on my magnifier glasses and started drawing the lines. I think they turned out good, though probably pointless because you cannot see the lines when gaming with them.
Not exactly what makes the best coloured pencil to use (type or brand). The Prismacolor ones are soft and have good wax content. A sharp point is certainly key to getting into all the parts of the figure.
Side note, I have ordered a bunch of American and Filipino miniatures from the 1898 Miniatures company for a future skirmish battle using The Men Who Would Be Kings rules.