1. Begin with two layers of your base colour. Allow to dry.
2. Using a striper brush, carefully paint two upside-down triangles on the tip in your chosen colour.
For a refresher on how to use striper brushes, click here. Do two coats of this, if you're using a light colour.
4. Allow to dry, and then use your next colour to fill in triangles from the cuticle with a striper brush - to about halfway up the nail.
So you'll have a little band of zig-zags in the middle.