I like to use a salad dressing bottle to mix this formula. In any event, you will need a container that closes tightly and won't leak if you shake it.

Mix corn syrup and water, add food colorings, cover and shake to mix. Add the sifted cornstrach and shake well again. If any lumps remain, let the bottle site for a few seconds, they will rise to the top and you can skim them off. Store in the refrigerator, don't make too far in advance as this only keeps for a couple of days.