Painting can be done on cakes, cookies, and cupcakes.  I prefer to paint on fondant or a crusting buttercream and love the artistry of "edible paint".  Buttercream gives texture to the "painting" much like oil based paint does to a portrait.  Watercolor painting is softer and perfect for a shower or wedding cake design.   Another form of "painting" on a cake is with a watercolor look for the base color.  It's easy and looks really pretty when 2 or 3 colors are semi-blended together.  Perfect for just a splash of color.  I also like to paint in buttercream with a spatula for a thinker textured look.  Consider painting when we design your dessert.  It's sure to be a showstopper!