It won't take much for that small of a quantity, but you need to make sure you don't use baby powder or anything that might have fragrance, skin softeners, additives, etc. in them.
Can I ask how big the piece or area is you are painting? You could always shoot the whole area with a flat clear.
How custom of a color is it? OneShot poster colors dry dead flat, and have a good array of colors, but they are mostly primary colors.