Start by making the cake mix as you usually would by combining the butter and sugar followed by eggs, oil, and vanilla, before finally folding in the dry ingredients.
Make the frosting by creaming together the bugger, sugar, vanilla, and salt. Whip until nice and fluffy. Divide frosting into bowls for however many colors you'd like to make. Add food coloring to the bowls and mix again.
Pipe a line of each color of frosting straight down a sheet of plastic wrap. Repeat all colors in one line. Roll into a log and add to a large piping bag with a large star tip.
Frost the tops of the cupcakes by first frosting a bit of white to cover the top and then frost on the rainbow. Add mini marshmallows for "clouds" or simply use more of the white icing.