Cooking shows such as "Ace of Cakes" have shown just how versatile cakes can be. Some of them can even be painted. A painted cake should be done over frosting covered with fondant. Fondant lends itself to better designs. You also need to have your design idea before you start the cake. Use the image as a guide for the artwork on the cake.
Apply a thin layer of frosting over the entire cake. Let this dry for 20 minutes.
Prepare the fondant according to the package directions. Roll out enough to cover the entire cake. Smooth out the fondant so no bubbles remain. Cut off any left over fondant.
Using a toothpick or wooden skewer, do a very light outline of the drawing on the cake's surface. This can also be done with a cookie cutter. Press just enough on the cake's surface to leave a slight impression.
Test the food coloring on a spare patch of fondant. It can be dark straight from the bottle and could react poorly with the fondant. You need to know if you need to lighten any colors before you start the final painting.
Dip a paintbrush into the food coloring and carefully apply the color over the fondant.
If needed, fill a pastry bag with tinted frosting and fit it with a fine tip. Pipe outlines around your painted designs to make them stand out more.