Preheat the oven to 350F; line 12 regular muffin cups with liners, set aside.

In a medium bowl, whisk together the flour, baking powder, and salt. In a (slightly large) measuring cup, mix together milk, egg whites, sour cream, and vanilla, whisking until completely incorporated.

In the bowl of a stand mixer, beat together butter and sugar until very light and fluffy, 8-10 minutes.

Add in the flour mixture in three additions, alternating with the sour cream mixture, starting and ending with the flour, and beating on low in-between additions.

Divide batter into several small bowls, as many as the colors you want to do. I did 5 colors, so I divided the batter equally into 5 containers. Add in food coloring to the divided batter until you reach the desired coloring.

Drop batter by spoonfuls into the prepared muffin pan, layering colors. If desired, swirl using a toothpick.

Bake cupcakes for about 20 minutes, until a tester inserted in the center comes out clean. Let cool completely, then top with some powdered sugar (or white frosting) and enjoy!