In a bowl, mix 2-3 drops of blue food color in buttercream frosting.

In another bowl, mix 2-3 drops of pink food color in buttercream frosting.

Fill both frostings in separate piping bags and cut there tips with a scissors.

Place both the piping bags inside a piping bag fitted with star nozzle.

Pipe the frosting on top of the cupcake to make frosting spirals.