Set out 2 - 13x9 pans or dishes (you can also use 4 - square pans). Set aside.
In a medium bowl, combine the 2 boxes of lime gelatin with 2 cups of boiling water.
Stir until the gelatin is completed dissolved.
Pour that mixture into the prepared pan.
Repeat with the 2 boxes of the cherry gelatin and pour into the other pan.
Place the pans into the refrigerator to set for about 1-2 hours.
Lightly spray another 13x9 glass dish with cooking spray.
In a medium bowl, stir together the unflavored gelatin and 2 cups of hot water until completely dissolved.
Stir in the sweetened condensed milk.
Let set until mostly cooled down, about 20 minutes.
Meanwhile, remove the red and green gelatin from the refrigerator and cut it into small cubes, about 1-inch square pieces.
Evenly place the gelatin cubes in the prepared 13x9 pan.
When the milk and gelatin mixture is cooled, carefully pour it over the red and green cubes in the pan.
Place the pan in the refrigerator to set for at least 4 hours.
Once set, cut it into bars and serve.
Store the leftovers in the refrigerator.