Standard crayons are 3.5 inches in length and made mostly of petroleum paraffin wax. Paraffin wax is heated and cooled to achieve the correct temperature in which a usable wax substance can be dyed and then manufactured for use around the world. Paraffin waxes are used for cosmetics, candles, for the preparation of printing ink, fruit preserving, in the pharmaceutical industry, for lubricating purposes, and crayons.
I'd stick with wax crayons. I don't know if anybody makes plastic crayons.... but go ahead and spend the whole quarter
and get the good stuff.
I have not tried nor read about using soap dye. I do know that several of the guys over at castboolits forum use crayons and candle coloring chips in their lubes with happy results though.
Just get out and shoot!
Christmas is nearly here and it's really too late to order either product anyway. And for the next 3 months I'll have to explain to people why my lube is either red or green.