Whether you’re icing cupcakes for a “Fifty Shades of Gray” party or working on the creation of a child's robot cake, all you need to make gray frosting is your favorite white icing and black food coloring. For best results, use a liquid paste or gel food color.
It's Black and White
Gray frosting is made by adding a few drops of black food coloring to white icing. Liquid paste or liquid gel color mixes easier and yields faster results. Add one or two drops to begin with, and mix thoroughly. For a darker shade of gray, add additional drops of food coloring. Make sure you begin with enough white icing to cover your entire creation so that you end up with the same shade of gray in the end -- unless, of course, your goal is 50 shades of gray.