How do I get that smooth look, like the Star Wars cake CK-418C?
That technique is called Color Flow. Simply take royal icing and add the desired color. Add a small amount of water. Continue to do this until the icing in a nice runny, smooth consistency. Outline whatever it is you want to fill in with the color flow icing. Fill in the design with the loose icing. This will give you the smooth, clean effect you are looking for.
