Preheat oven to 350 degrees.

Grease muffin tins or line with paper cups.

In a medium bowl, whisk together flour, baking powder and salt.

In a large bowl, whisk together sugar, eggs, vegetable oil, milk and vanilla. Pour in dry ingredients and stir until just combined.

Divide batter evenly into 6 small bowls.

Add about 1/2 teaspoon food coloring to each bowl to mix red, orange, yellow, green, blue and purple batters. Stir well, so no streaks of white batter remain. Saturated colors look best.

Starting with the purple batter, drizzle a forkful of batter into each of the muffin cups (just over 1/2 tablespoon of each color). Repeat with remaining colors, working to blue, green, yellow, orange and red. Drizzle each color of batter on carefully but don't worry about spreading the layers of color out as this may cause them to mix. Allow the batter to settle on its own.

Bake 15-20 minutes until a toothpick inserted into the center comes out clean.

Cool cupcakes on a wire rack before frosting.

Rainbow sprinkles are recommended.