Cook's Note: If you only have 1 mini cupcake tin, it is recommended that you mix up one batch of batter at a time and bake it off individually before mixing the next batter.
Preheat the oven to 350 degrees F. Line 3 (24-cup) mini cupcake tins with paper liners.
Evenly divide the cake mix into 3 medium bowls. In each bowl, add 1 egg white, 3 tablespoons oil, and 1/3 cup of one of the juices. Mix each for 2 minutes until the batter is well incorporated. Scoop the batter into muffin cups using a mini ice cream scoop or tablespoon measure, filling each a little more than half full. Bake until a toothpick inserted in the center of a cupcake comes out clean, 10 to 12 minutes. Remove from the oven. When cool enough to handle, place the cupcakes on a wire rack to cool completely.
In a medium bowl, beat together the butter with the softened cream cheese until combined. Slowly add in the powdered sugar until completely incorporated. Evenly divide the frosting between 3 bowls. Add the remaining 1 tablespoon of one of the juices to each and mix until well combined. Add a couple drops red food coloring to the cherry flavored, a couple drops blue food coloring to the blueberry flavored, and a couple drops yellow food coloring to the pineapple flavored. Mix until well combined
Place each icing into a resealable bag and snip off 1/4- inch from the bottom corners of each bag. Pipe each flavored frosting atop its corresponding cupcake. If the frosting becomes too soft, chill in the refrigerator until it firms up enough for piping. Garnish the top of each cupcake with its corresponding garnish.