Spray a 9×13 dish with non-stick cooking spray. Set aside.

Red layer: Combine 1 envelope unflavored gelatin and ¼ cold water in a medium bowl. Whisk slowly to dissolve gelatin. Let soak for 4 minutes. Add strawberry gelatin and 1 ¾ cups boiling water to the unflavored gelatin. Stir to dissolve strawberry gelatin. Set aside for 45 minutes or until cooled to room temperature. Pour into prepared dish and refrigerate for 1 hour or until set.

White layer: Combine sweetened condensed milk and 1 cup boiling water in a medium bowl. Whisk to mix well. Stir in nata and whisk to combine. Set aside.

In a separate medium bowl, combine 2 envelopes of unflavored gelatin with ½ cup cold water. Whisk slowly to mix well. Let soak for 4 minutes then add ½ cup boiling water. Whisk slowly to mix well. Add sweetened condensed milk and nata mixture and stir. Let cool for 30 minutes to room temperature. Add milk mixture over set strawberry layer. Refrigerate for 1 hour or until set.

Blue layer: Combine 1 envelope unflavored gelatin and ¼ cup cold water in a medium bowl. Whisk slowly to dissolve gelatin. Let soak for 4 minutes. Add blueberry gelatin and 1 ¾ cups boiling water to the unflavored gelatin. Stir to dissolve blueberry gelatin. Set aside for 45 miutes or until cooled to room temperature. Pour into prepared dish over set white layer and refrigerate for 6 hours to overnight.

Run a small knife around the edges of the gelatin. Slice into 12 squares. Transfer to a serving tray, decorate with sprinkles and serve.