ZEBRA cake instructions: just color half of white cake batter. Drop 2-3 tbsp of first color into center of cake pan, then do the same with the other color, making concentric circles. Keep layering the colors on top of each other. The batter will spread out on its own but once in a while you might need to tap the pan on the counter to help it along. If you don't get it to spread evenly, it won't bake evenly.
The popular recipe, featured in the January issue of Cosmopolitan magazine, is less than 100 calories for the entire cake, and it can be all yours in under five minutes: http://chocolatecoveredkatie.com/2015/01/13/low-fat-banana-breakfast-cake-mug/