When using gel-based food coloring, a little goes a long way. Use a toothpick or a small skewer to dab in a tiny drop of coloring at a time. Avoid using complementary colors in a single batch, as they will mix to brown in the piping bag.

To fill a piping bag, insert a piping tip and push it to the end of the bag. Then using a paring knife or scissors, make a cut at the end of the bag so the thin end of the piping tip pokes out through the cut, while the wide end of the tip is held in place by the bag. Twist the plastic of the bag just above the piping tip to make a temporary seal, then insert the bag into a drinking glass. Fold the top of the bag over the lip of the glass, this will keep the outside of the bag clean while you fill. Pour your filling into the bag. (The twist you made earlier should keep the filling from squirting out of the piping tip.) Remove the bag from the glass. Twist the top closed. Untwist the bottom when you are ready to pipe.

Instructions

Step 1   
In a medium bowl, stir together the confectioners’ sugar, 2 Tbsp water, and the corn syrup with a rubber spatula. Add more water drop by drop, until the mixture is the consistency of shampoo and forms a ribbon when it flows off the spatula into the bowl. Divide mixture into three small bowls. Tint each with food coloring as desired.

Step 2
Fit a piping bag with a very small round tip, such as an Ateco #1. Fill the bag with the lightest color first. Pipe thin lines across parchment-lined baking sheets; you’ll need 2 or 3 sheets, depending on how closely together you space your lines. When the bag is empty, fill with the next-darker hue and continue piping. Repeat with the remaining color. Let stand at room temperature, uncovered, in a dry spot until the sprinkles have hardened, at least 8 hours or overnight.

Step 3
Use your hands to break the sprinkles off the parchment paper and into small pieces. Toss together and store at room temperature in an airtight container.