Prepare yellow cake mix according to bag directions. Scale 2 lbs batter into sprayed 10” baking pans, repeat at least 2 more times to make 3 cakes total. Bake at 350°F for 40-45 minutes or until cake springs back lightly when touched. Let cool completely and depan. Stack, fill, and crumbcoat with white buttercream. At the base of the cake, pipe a ring of light blue buttercreme. Combine white and light blue buttercreme icings, creating lighter blue colors as the rest of the cake is iced. Using russian tips, load piping bags using a combination of the rest of the buttercreme colors, combining colors in each bag as desired. Pipe a ring of flowers around the top edge of the cake, fill in with light green buttercreme leaves.