Mix the cake batter according to the box directions. Be sure to line your muffin tins with colorful cupcake liners to match your vibrant theme.

Divide the batter evenly among six bowls. Add a few drops of food coloring to each bowl, creating the rainbow’s colors—red, orange, yellow, green, blue, and purple. Stir gently until blended.

Place each colored batter in separate quart-sized Ziploc bags. Seal them almost all the way, leaving a small opening for air to escape. Snip off a tiny corner of each bag for easy pouring.

Starting with purple, layer the colors in reverse rainbow order in the cupcake liners: purple on the bottom, then blue, green, yellow, orange, and finally red.

Bake according to the box directions until a toothpick inserted comes out clean, usually around 18-22 minutes. Let them cool completely in the tins.

In a mixing bowl, beat the softened butter and marshmallow creme together until smooth. Gradually mix in the powdered sugar, vanilla, and salt until you reach a fluffy consistency.

Use a piping bag or a simple spatula to frost the cooled cupcakes with your dreamy marshmallow frosting.

Top each cupcake with rainbow sprinkles, or place an Airheads Extreme in a rainbow arch. Optionally, crown them with a white chocolate Reese's Peanut Butter Cup!

Store the decorated cupcakes in the refrigerator for about 30 minutes to help the frosting set before serving.