Step 1Generously dust a large, wax-paper-lined baking sheet with the powdered sugar and set aside.
Step 2In the bowl of a stand mixer, or in a large mixing bowl, gently sprinkle the gelatin over 3 tablespoons of the water and set aside.
Step 3In a large saucepan, stir together two-thirds cup of the granulated sugar with the corn syrup, salt and remaining water until you have a wet, sandy consistency. Clip a candy thermometer to the inside edge of the pot and cook over medium-high heat, without stirring, until the thermometer registers 245 degrees Fahrenheit. Immediately remove the pan from heat.
Step 4Using the whisk attachment, or with a hand mixer, begin whisking the moistened gelatin on medium speed. Carefully add the sugar mixture in a slow, steady stream. Once incorporated, add the vanilla and increase the speed to medium-high. Continue whisking until the marshmallow mixture is at least doubled in volume, very white and sticky, and when the beater is lifted the mixture remains in soft peaks, 4 to 6 minutes.
Step 5Fold down the tops of two large resealable plastic bags. Spoon about three-fourths of the marshmallow mixture into the corner of one bag. Twist the bag to seal (as with a piping bag), then set aside. Add a few drops of food coloring to the remaining mixture and quickly stir until you have the desired shade of yellow. Spoon this mixture into the corner of the remaining bag and twist the bag to seal.
Step 6Snip the tips off each bag to form an opening roughly one-fourth inch wide. Using the white marshmallow mixture, gently pipe 2- to 3-inch daisies onto the prepared baking sheet, spacing them about 1-inch apart. Keep a small bowl of water nearby and moisten your fingertips to pinch the marshmallow to release them it the piping bag (the water will keep your fingers from sticking to the mixture). Pipe a dot of the yellow mixture into the center of each daisy.
Step 7Generously sprinkle the daisies with the remaining 3 tablespoons granulated sugar to coat, then set them aside in a cool, dry place until set and easy to handle, several hours.