Combine sweetened condensed milk with 1 cup boiling water. Sprinkle 2 envelopes unflavored gelatin over ½ cup cold water. Let stand a few minutes to soften and then add ½ cup boiling water and stir until dissolved. Add gelatin mixture to the sweetened condensed milk mixture and stir to combine. Cool to room temperature. Pour over blue gelatin layer. Refrigerate for 30 minutes or until almost firm.