1 C sour cream
1/2 C milk
1/3 C vegetable oil
Combine all ingredients until incorporated (about 30 seconds). Scrape sides of bowl and then beat on med-high speed for 3 minutes.
Divide batter according to how many colors you are using.
Use food coloring to color batter to desired intensity. I used a 1/4 t and they were very bright!
To get a stripe like I used, you'll want to put a spoonful of each color in the cupcake one at a time. The batter is thick, so it won't spread on it's own. A great tip is to set out a little bowl of water where you're working. Dip your finger in the water and then gently spread the batter out. The water will make it so the batter doesn't stick to your fingers.
Another tip is to use a measuring spoon and some water to measure out how many teaspoons/tablespoons are going to fit in your cupcake. Then divide that by how many colors you have so you know how much of each color to use for each cupcake.
Bake them according to the package directions, until a toothpick comes out dry
Let them cool and frost with THIS frosting!