Spray a 9x13 dish with nonstick cooking spray.
Dissolve half of a packet (1 tsp) of unflavored gelatin and a packet of Red Jello in boiling water. Dissolve the unflavored gelatin first, then add the Jello.
Pour the Red Jello mixture into the bottom of a 9x13 dish and refrigerate for 30 minutes to set.
Mix a packet (2 tsp) of unflavored gelatin to one cup of boiling water and dissolve. Add a can of condensed milk to the gelatin mixture and let it cool while Jello is setting in the refrigerator.
Pour one up of condensed milk mixture and make sure it covers the Jello layer completely. Cool for 30 minutes in the refrigerator on a level surface.
Make a batch of Orange Jello and gelatin and let cool while the creamy layer is setting. blue jello being poured in a pan
Pour the Orange Jello layer over the creamy layer, and cool for 30 minutes on a level surface in the refrigerator. Repeat with the rest of the Jello Flavors and milk layers until all layers of Jello and milk are set.
When the last layer of Jello is poured on top, allow the whole dessert to cool in the refrigerator for at least an hour.