To create tricolor stacks of marshmallows, make this recipe three times, using a different food coloring each time.
Sprinkle gelatin over 1/3 cup water in a mixer bowl, and let stand until softened, about 5 minutes. Coat an 8-inch-square baking dish with spray, line with parchment, then spray parchment.
Bring remaining 1/4 cup water and the sugar to a boil in a small saucepan over medium-high heat, stirring until sugar dissolves. Wipe sides of pan with a wet brush to prevent crystals from forming. Boil for 2 minutes. Remove from heat; stir into gelatin. Attach bowl to mixer; whisk on medium-high speed until thick and cool, about 10 minutes. Once syrup begins to look white, after 3 to 4 minutes, add food coloring, a drop at a time, to reach desired color. Whisk until sticky but pulling away from sides. Spread in prepared dish. Cover with plastic wrap. Let stand until firm, at least 7 hours or overnight.
Place confectioners' sugar in a medium bowl. Cut out marshmallow rounds using a 1 1/2-inch cutter coated with spray. Toss with sugar, tapping off excess.
Repeat with other food colorings. To assemble towers, thread marshmallow rounds onto a skewer, and serve.