For the tails: Place the small green gumdrops on the work surface standing upright. Cut each gumdrop in half by cutting straight down with a sharp knife.
To assemble: Frost each cupcake with about 2 tablespoons buttercream. Place the green sanding sugar in a small bowl. Invert each cupcake into the sugar and press gently to adhere.
Stick a green jelly bean straight into the frosting for the head. Using a #2 round piping tip, pipe on 2 buttercream eyes. Then dip a toothpick into the black or brown food coloring gel and create the pupils for the eyes. Push the flippers into the edges of the cupcake frosting. Attach a half gumdrop tail between the back legs. Pipe a little frosting onto 7 green and 7 brown candies before gently pressing them into the frosting on the "back" of each turtle to make the shell. Repeat steps for all cupcakes.
Chill your candy-covered chocolates to stop the warmth of your fingers from melting them during assembly.