The Pellets in some Pellet Posies will flash different colors, and will often change from the color you want by the time your Pikmin have destroyed the Posey. Instated of swarming your Pikmin around the stem, stand in front of the Pellet Posey until the Pellet changes to the color you want. Then, throw a Pikmin at the Pellet itself. This will automatically destroy the Posey. This trick works best with Yellow Pikmin.