Stir together the powdered sugar and flour. In another bowl, place 2 whites and add the color. Pour on the sugar/flour mix.
In a pot, whisk together the sugar and water. Stir until the mix comes to a boil and becomes a syrup.
Whip the two remaining egg-whites to a light mousse and pour the boiling syrup on them. Keep whisking to get a meringue. Let it cool before adding it to the first mix.
Fill a pastry bag and form 1-inch rounds on a tray covered with baking paper. Let dry 30 minutes.
Preheat the oven at 320°F. Bake 14 minutes, remove from the oven and let the shells cool.
Fill the shells with a nut of your favorite Woos, Strawberry, Raspberry, Passionfruit or Lemon and enjoy.