Preheat the oven to 375 degrees F.
Combine the softened butter, sugar, egg whites and vanilla mixing well. Slowly fold in the flour, salt and baking powder. Lastly, add the milk ,continuing to stir.
Pour into greased muffin tins (or liners) and bake 20-25 minutes. Insert a toothpick around 20 minutes and if it comes out clean they're done!
Add a few drops of blue food coloring to the white frosting and mix well.
Generously frost each cupcake and set aside.
Open the Wilton Rainbow kit and carefully bend the rainbow candy one at a time and place on top of the cupcake, gently pressing down.
Next, take 2 cloud candies for each cupcake and place them next to the rainbow on either side.