Use a wooden spoon to completely combine the marshmallows and butter, and pour over the cereal in one of the containers. Stir until the cereal is completely mixed with the marshmallow mixture, you’ll see it turns sticky. Transfer the mixture to the greased mold, wet your hands and use them to press the corners until you have a square block of cereal. Repeat with the 4 remaining colors. Place the colors side by side.