Lightly spray a 9x13 baking dish with cooking spray. Use a paper towel to remove any excess puddles that may have formed. You just want a light coat.
In a small mixing bowl, whisk together the contents of one of the orange jello packets (reserving the other for later) with half of a packet (1 and 1/4 teaspoons) of gelatin. Add one cup of boiling water and whisk until dissolved. Cool for 10 minutes so it is not boiling hot.
Pour the contents into the bottom of the prepared dish. Place in the fridge to set for 15 minutes.
While the jello is chilling, make the condensed milk layer. In a medium mixing bowl, whisk together the sweetened condensed milk with 1 cup boiling water. In a small mixing bowl, stir together the room temperature water with 2 packets (5 teaspoons) of unflavored gelatin. Let stand for 3 minutes to bloom. Once bloomed, pop in the microwave for 20 seconds on high to liquify the gelatin. Whisk the gelatin mixture into the sweetened condensed mixture and let cool until room temperature.
Pour 1/3 of the cooled sweetened condensed milk layer over the orange jello layer. You’ll be using approximately 3/4 cup of the milk mixture per layer. Place the dish in the fridge to set for about 20 minutes. It takes a bit longer to set the white layer.
While the milk layer is setting, we’ll get started on the black layer. In a small bowl, whisk together one box of grape jello, 1 packet (.25 oz or 2.5 teaspoons) of unflavored gelatin, 1 cup of boiling water and 1/2 teaspoon of black food coloring. If the jello isn’t dark enough for you, simply add another 1/4 teaspoon of food coloring. Cool until it reaches room temperature.
Pour the grape jello layer over the set condensed milk layer. Place in the fridge to set for 15 minutes.
Once the grape layer has set, pour another layer (1/3 of the mixture) of the condensed milk mixture. Place in the fridge to set for 20 minutes.
Repeat step 2 & 3 with the second box of orange jello. Chill for 15 minutes.
Once set, pour the last of the condensed milk mixture over the final orange layer. Chill for 20 minutes.
Lastly, repeat step 8 with the second box of grape jello. This will be your final layer. Once all the layers are complete, place the layered dessert in the fridge for at least one hour but up to overnight.