Using a small whisk, mix flour, baking powder, oil, milk, sugar, vanilla and peppermint in a small bowl until no lumps remain. Pour half of the batter into a separate small bowl. Add food coloring to one of the bowls of batter and mix until it turns uniformly red.
Very lightly grease the bottom of a microwave-safe mug. Pour 1 1/2 tbsp of plain batter into the center bottom of mug. Add 1 1/2 tbsp of red batter directly on top, also in the center. Don't worry if batter doesn't yet reach edge of mug. As you continue to add more layers on top, the bottom layers will spread out and you'll see alternating circles of the two colors. Continue with remaining batter, alternating between the two colors until you run out of batter. Cook for about 1 minute. Top of cake should be dry to the touch.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.