In the bowl of a stand mixer, whisk together the gelatin and ½ cup of cold water. Let it sit for 10 minutes to bloom.
In a saucepan over medium heat, combine the remaining ½ cup of water, sugar, corn syrup, and salt. Stir and let it simmer for 6-8 minutes until the sugar dissolves.
Slowly pour the hot syrup into the gelatin mixture while mixing on low speed. Once combined, increase speed to high and whip for about 10 minutes until thick and fluffy.
Add the cotton candy flavoring and mix for another minute. Divide the mixture into two bowls, adding pink food coloring to one and blue to the other. Gently swirl together.
Grease a 9x13-inch pan and dust with powdered sugar. Pour in the marshmallow mixture, smooth the top, and let it set at room temperature for 8-12 hours.
Once firm, remove from the pan, cut into squares, and roll in powdered sugar to prevent sticking.