Colored egg yolk glazes (also called egg tempera) are a great way to decorate sugar cookies. They’re made by mixing small amounts of beaten egg yolk with food coloring, and you paint them on the cookies before they are baked. The colors after baking are bright and true, says kittyfood. The glaze doesn’t add any sweetness, but you can sprinkle decorative sugars over the glaze before baking the cookies, or outline the designs with icing after baking. Be sure to have plenty of inexpensive paint brushes, or even Q-tips, for applying the glaze. It’s an excellent cookie-decorating medium for children, who become absorbed in creative cookie painting, notes Rhee.