Stir one box of Jell-O with 1 cup of boiling water until dissolved. Add 1/2 cup cold water. Layer into your desired containers and place into the refrigerator until set.
Combine the sweetened condensed milk with 1 cup of boiling water.
Stir 1/2 cup cold water and your unflavored gelatin until dissolved. Mix into the sweetened condensed milk. Layer over the set green layer.
Continue until you reach the top. Mix together the additional box of Jell-O if necessary.