Prepare each flavored gelatin separately: In a bowl, mix 1 box of flavored gelatin with 1 cup of boiling water. Stir until completely dissolved, then add 1/2 cup of cold water and mix well.

Pour the prepared flavored gelatin into individual rectangular or square containers. Chill in the refrigerator for at least 4 hours, or until completely set.

Once the gelatin is set, cut it into small cubes and set aside.

In a large bowl, dissolve the unflavored gelatin in 1/2 cup of cold water. Let it sit for 5 minutes to bloom.

Add 1/2 cup of boiling water to the unflavored gelatin and stir until fully dissolved.

Stir in the sweetened condensed milk and mix until smooth. Let the mixture cool to room temperature.

Place the gelatin cubes into a large pan or mold, arranging them to mix colors randomly.

Pour the cooled sweetened condensed milk mixture over the gelatin cubes, ensuring it fills the spaces between the cubes.

Refrigerate the entire mixture for at least 4 hours, or until fully set.

Once set, cut into squares or slices and serve chilled.