Divide frosting into 3 small bowls. Leaving 1 portion white, stir red and green food color into remaining portions. Frost each cookie with about 1 tablespoon red or green frosting. Frost about 1 inch of short side of each triangle with about 1 1/2 teaspoons white frosting for hat brim. Sprinkle brims with coconut. Place marshmallows on ends of hats for tassels. Let stand until set before storing.