Have an airbrush machine just for baking. Be certain that it is always clean. Cover the surface where you will be working as the color will fly. Cover around the cake and behind the cake. You can use newspaper, butcher paper or a disposable tablecloth. Pressure, angle and speed are very important when using an airbrush. It is best to practice. The more practice, the more comfortable you will become with the airbrush. Draw what you are going to put on the cake to use as a guide. Put just a bit of color into the airbrush. Don't over fill as it will spill out on the cake. In between each color wash the brush out with hot water. To make colors more intense, go over the color several times. Airbrushing works good on butter cream icing. Enjoy your masterpiece.