When you say closed cell foam, if you are talking EVA (flip flop, kids' toys) paint/color is strictly optional. With styrofoam I am guessing you are using a building grade or better product. If so you might want to consider dunking the body before adding the hook in a latex paint, that will seal it so you can then use spray paint or solvent based color with care. As Hap stated an epoxy type finish is the ultimate finish available to most of use. You will find water based art and craft paint remarkable durable. I mostly use that for highlights.