Start with a base color. I used China Glaze's Make Some Noise.
After that is dry, get some saran wrap. You are going to need one little piece for each nail you are doing. Paint on your second color (I used China Glaze Aquadelic) and while it is still wet, dap the piece of saran wrap onto your nails to get the desired effect. Finish with a top coat and you will have something like the bottom picture!