I remember having to 'crayon' in my D&D dice back when.
Missing some color in one of your dice?
Get a crayola uber box and fill in the missing thumb of your Thing and Sidekick dice is not such a bad "thing", huh huh huh
I'd rather use a marker. The "waxy" quality of crayons could be seen as "marking" dice in the tactile sense, or messing with the weighting for rolling/randomness purposes.