To create multi-colored tie-dye or rainbow swirled frosting, lay out a sheet of plastic wrap, place parallel rows of different colored icings side by side, roll them into a tight log, twist the ends, snip one end, and drop the log into a pre-tipped piping bag.
Make the Icing
Make it: Use your favorite recipe to create your icing
Divide it: Depending on the number of colors you would like to incorporate, evenly separate the icing into bowls.
Mix it: Add your food coloring and stir until completely combined.
Add it to piping bags: Use my cup method to add each color icing to a separate piping bag. Snip the tip of the bag, but do not add a decorative tip.
Prepare the Multi-Color Log
Lay out the wrap: Spread a clean sheet of plastic wrap flat on a clean counter top.
Arrange the colors: Pipe your different colored icings in straight, parallel lines right next to each other on the plastic wrap.
Roll it up: Gently roll the plastic wrap forward to enclose the icing into a log (like a burrito), making sure not to smash or over-blend the parallel lines.
Twist the ends: Twist both ends of the plastic wrap tightly to secure the icing and eliminate air pockets.
Loading and Piping
Snip the end: Cut off just one of the twisted ends of your plastic wrap log with scissors.
Insert into the bag: Drop the log into your master piping bag (fitted with your favorite piping tip) with the snipped end pointing down toward the metal tip.
Test the swirl: Squeeze the top of the piping bag until the multi-colored frosting starts coming out uniformly through the tip.
Because your colors are separated into different piping bags. You can repeat this technique using different color combinations, like shown above.