I made my cupcakes and frosting (this is a great frosting recipe!) and dyed half of the frosting blue. Then I used a long cake decorating tip and filled it with the blue frosting.
Then I placed it in the center of each cupcake (make sure you don’t go all the way down to the bottom). The icing can come out the bottom. So just over half way, squeeze the frosting into the cupcake for about 3 seconds and pull it out. I then wiped away any excess frosting that was on the top of the cupcake.