Press crisped rice cereal treats mixture 1 in. deep into prepared 10 1/2 x 15 1/2 in. Jelly Roll Pan; unmold onto waxed paper. Imprint treats with Ice Cream Cone Plastic Cutter and cut cones with paring knife.
Tint White Candy Melts® with Primary and Garden Candy Colors. Cover scoop area with melted candy in cut bag; spread with spatula. Sprinkle with Rainbow Jimmies. Let set.