Use this simple icing on our Marbled Iced Sugar Cookies.
Mix sugar, water, and meringue powder with a mixer on low speed until smooth, about 7 minutes. Icing should be the consistency of glue. (If icing is too thick, mix in a little more water. If icing is too thin, add more confectioners' sugar). Divide icing and work in batches. Add food coloring, 1 drop at a time, until desired color is achieved; Use immediately.