Melt candy coating disks according to package directions. Meanwhile, spread cereal in an even layer in a small rimmed baking pan. Coat cereal with color spray, stirring gently between coatings, to cover as much cereal surface as possible.

Spread a thin layer of the melted candy coating over 1 sugar cone using a spoon or offset spatula. Roll cone in tinted cereal to coat, gently patting to adhere. Stand cone up on a large sheet of parchment paper. Repeat process with remaining 7 cones. Let cones stand until coating sets, about 10 minutes. (Spray cones lightly with color spray if needed to even out green coloring.)

Spoon 1/4 cup of the remaining melted candy coating into an unsnipped piping bag (and not fitted with a piping tip); microwave on MEDIUM (50%) until candy re-melts, about 30 seconds. Snip a small hole in corner of piping bag. Pipe small dots onto cone trees; adhere candy sprinkles to dots as desired. Store, covered, at room temperature up to 3 days.