I too would like some colour. My moustache is blond-turning-grey, so some colour would help define it a bit.
Would Wacky Tacky add any colour to a light coloured 'tache like mine?
Good idea about the crayons, but I'm guessing that crayons are just wax and food colouring. So why not just add food colouring?
Crayon or food colouring, would it be rainproof? (Not that I've seen much rain lately!

)
Cheers,
Guz