Scoop one tub of vanilla frosting into a bowl. Add red gel food coloring using a toothpick or wooden stir stick. Start with a very small amount.
Mix the red frosting with a spoon. Add more food coloring if needed (using a clean toothpick!), until you're happy with the color.
Scoop another tub of frosting into a second bowl. Using the same technique as above, add blue gel food coloring and stir until you're happy with the color.
Cut off the tip of the piping bag (if using disposable).
Insert one piece of the coupler into the tip of the piping bag. Insert the icing tip into the other piece of the coupler, then screw it in place onto the piece on the piping bag.
Fill your piping bag with the white frosting.If you have more than one star tip or are using couplers, you can repeat this process now with the red and blue frostings. If you are using a single tip with no coupler, wait until you are finished with the white frosting before filling the red and blue bags.
Step 2: Frost cupcakes
Starting at the bottom of the cupcake, pipe one row of white stars.To pipe a perfect star, hold the piping bag vertically and squeeze from the top of the bag (farthest away from the tip). Apply pressure while holding the bag still, and then release the pressure as you pull the piping bag straight up off the cupcake. The more pressure you apply, the bigger the star.Pipe two other partial rows of white stars, leaving space between them for the red stars. Don't complete these rows: leave a space on the left for the blue portion of the flag.
If using the same icing tip, remove it from the white bag and clean it before attaching it to the bag with red frosting.Using the same technique as the white stars, make one full row of red stars and two partial rows.
Remove the icing tip from the red bag, clean it, and attach to the blue frosting bag. Pipe several short rows of blue stars in the remaining space.
Add the white star sprinkles to the blue corner of the cupcake.
Your 4th of July cupcakes are complete!
Video
Notes
The icing colors will get darker the longer they sit after the food coloring is added. Feel free to make these cupcakes the night before and you'll wake up to slightly brighter colors in the morning.