Prepare cupcake batter using cake mix, 1 cup buttermilk, 1/3 cup oil, and 4 eggs. Bake as directed on box. Let cupcakes cool completely.
Transfer each can of frosting to a bowl. Using icing colors, tint one bowl pale green and one pale yellow. Using a small metal spatula, frost cupcakes. Roll edges of cupcakes in nonpareils. Insert a photo flag into the center of each cupcake.