I saw a picture that gave me this idea. I found a really pretty neutral color for the base, any would do, the more opaque, the easier it will be.
Pick the color's you'd like for you dots, at least 3, but as many as five would work. I chose white, lime green and purple. Dot on the first color, and try to do some bigger, some smaller, work in a curve around a corner.
Keep adding more colors, take a pause to let each one dry a bit so you don't smear. When you've gotten the effect you like, let dry, and then add your topcoat! Voila!!