Place 4 sheets of parchment paper onto your countertop. Prepare a disposable piping bag with small round tip (#4). Have 3 more disposable piping bags handy for the various other colors.
In a medium-sized bowl, stir together the erythritol, arrowroot starch and salt. Stir in the water and vanilla paste. The mixture should be like a very thick, dense dough.
Divide the mixture into 4 small bowls. Stir in one food coloring per bowl. Mixtures should look like frosting, they should not be runny or liquidy. Scoop one bowl’s mixture into the prepared piping bag.
Pipe half of the mixture as lines and the other half as small dots/confetti (use 2 sheets of parchment paper for the lines and the other 2 sheets for the confetti). When you run out of one color, rinse the piping tip, place it in a new disposable piping bag, and then fill the bag with the next color. Repeat this until all mixtures are used up.
Let the lines and confetti sit uncovered at room temperature for at least 12 hours in order for them to dry and firm up. Carefully slice the rainbow lines with a knife, or pick them up and gently break them with your thumb and forefinger.
Pour the sprinkles into a tightly sealed container (I used a 16oz mason jar). Gently push the confetti off the parchment paper with your finger. Pour the confetti into another container (I used another mason jar). Store the sprinkles and confetti in the tightly sealed containers in the fridge for up to 2 months.