Start by preparing your work area, gel food color can easily stain your working surface so cover it with parchment paper or plastic wrap.
Fix a piping bag with a large star tip, or any other piping tip that you like. Set aside.
Cut about 15 inches of plastic wrap and place it on the counter. In the middle of the plastic wrap add about 1/3 of the blue buttercream, spread it into a 6x6inches square. Top it with 1/3 of the white buttercream, and carefully, spread it on top of the blue square. Top it with 1/3 of the red buttercream, and carefully, spread it on top of the white square.
Before adding the buttercream to the plastic wrap take a look at the piping bag you will be using, some are smaller and some are larger, so make sure the square that you are making is not larger than the piping bag, as it won't fit in when rolled.
Roll the wrap, so it forms a tube, and place the wrapped buttercream inside the piping bag. Do a first, pipe and dump test, so you get the buttercream closer to the tip.
Pipe the buttercream onto the cupcakes and decorate with sprinkles and cupcake toppers.
Repeat with the rest of the buttercream and cupcakes.
Refrigerate cupcakes at least one hour before serving.
Store in the refrigerator for 3-4 days.