Frost each cupcake with a thin layer of vanilla frosting and refrigerate for 1 hour to make decorating easier.
Add 1 or 2 drops blue food coloring to the chocolate frosting to make it darker. Fill a piping bag fitted with a small round tip with the darkened chocolate frosting and draw the outline of a small pentagon shape on the top of each cupcake. Fill in the pentagons with chocolate frosting. Starting at the points of the pentagon shapes, draw lines halfway toward the edges of each cupcake. Draw a triangle at the bottom of each line, connecting one of the corners to the line, to indicate partial pentagon shapes around the edges of each cupcake. Fill in triangles with chocolate frosting.
