In a large pot, melt butter. Add marshmallows and stir until melted.
Separate about 1 cup of the marshmallow mixture into a smaller pot. Add green food coloring to this smaller pot. This will be the pumpkin "stem". Turn off the heat and set this aside.
To the large pot, add the yellow and red food coloring to make orange. Add the remaining rice krispie cereal to this mixture to make the "pumpkin". Stir until well-coated.
Working quickly, make sure that you cover your hands with butter or spray with cooking oil (to prevent sticking) take approximately ½ cup of the the orange krispie mixture and make little balls. Place on tray that has been lightly sprayed with cooking oil to prevent sticking.
After all the pumpkins are made, return to the stove and turn on heat to warm the small pot of green melted marshmallows if necessary. Add 1½ cups of the rice krispie cereal to this small pot. Stir until cereal is well-coated.
Again, coat hands with butter or cooking spray. Make small "stems" and place them on top of each pumpkin ball. Gently press down to ensure they stick to the pumpkin.
Place about 1 tablespoon of the black icing into a small sandwich size ziplock bag. Cut a very tiny hole in the corner of the bag so that you can squeeze out a small amount of icing to decorate the pumpkin faces.
Store covered up to 2 - 3 days.
Recipe by Bebe Love Okazu at https://bebeloveokazu.com/2012/10/31/happy-halloween-pumpkin-rice-krispie-treats/