In a medium bowl, mix two boxes of red jello with 1 envelope of unflavored gelatin. Add 2 cups of boiling water and stir to dissolve. Cool to room temperature and pour into a 9x13-inch glass pan that has been sprayed with nonstick spray. Refrigerate for 15 minutes (make sure that your refrigerator is level, or your jello will come out uneven-looking).

While the first layer is setting, prepare the white layer. In another bowl, mix sweetened condensed milk with 1 cup of boiling water. In a separate small bowl, sprinkle 2 envelopes of unflavored gelatin over 1/2 cup of cold water. Let stand a few minutes and then add 1/2 cup of boiling water to dissolve the gelatin. Add to the milk mixture and stir to combine. Cool to room temperature. Pour this milk mixture over the first layer of red jello. Refrigerate for 30 minutes.

While the white layer is setting, prepare the blue layer. In a medium bowl, mix two boxes of blue jello with 1 envelope of unflavored gelatin. Add 2 cups of boiling water and stir to dissolve. Cool to room temperature and pour on top of the white layer. Refrigerate for 30 minutes.

Let jello set before cutting. Use a sharp knife to cut, and then use a metal spatula to slide underneath the jello and scoop out jello squares.