Line two baking sheets with silicone mats or parchment paper.
In a bowl, whisk the icing sugar, egg white and corn syrup with an electric mixer on low speed for 2 minutes or until soft-peaks form. Add a few drops of water or icing sugar as needed.
Divide the icing among 5 or 6 bowls. Add a small drop of food colouring to each bowl and mix until each colour is vibrant. Cover the bowls as you work.
Working with one colour of icing at a time, use a pastry bag fitted with a very small plain tip to trace lines quite close together on one of the baking sheets. Wash out the piping bag and repeat with the remaining colours until both baking sheets are covered.
Let the icing dry out for 5 hours or until the lines of icing easily come away from the silicone mats or parchment paper. Break the lines of icing into little sprinkle pieces.
The sprinkles can be prepared in advance. They will keep for 1 month in an airtight container at room temperature.