Source: Martha Stewart Living, December 2010
Beat 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 sugar.)
Beat in food coloring, 1 drop at a time, until desired color is achieved. If making more than 1 color, divide icing and work in batches.