Make the batter as instructed on the box.
Set the cones on a cookie sheet or in a cupcake cone baking pan, and fill the cones 1/2-3/4 full. Don't fill more than that. Bake per instructions.
While they're baking, work on the buttercream. Scoop the buttercream into a large mixing bowl. Add the drops a few at a time, and mix them in. Keep adding until you reach the desired color. Set aside in a cool place.
When cones are baked. Remove them form the oven, and let them cool about 10 minutes. Take a straight pin, and poke a few holes around the sides and bottom of the cones to release the steam.
Put you tip into the piping bag, then scoop the buttercream into the piping bag, or a baggie, and cut the tip. Give the buttercream a good squeeze to get the frosting to come down the tip. Refer to instruction in blog.
Swirl the frosting in a circle going around the cone, and giving the frosting height.
Then add your green stem/jelly bean to the top.