One day in advance, make sprinkles.
Prepare ½ recipe of royal icing following recipe instructions. Divide equally into seven portions. Tint each portion green, yellow, orange, pink, blue, teal and violet using icing colors. Prepare seven decorating bags with tip 2 and tinted icing. On parchment paper-covered board, pipe several lines in each color; let dry, about 3 to 4 hours.