For each flavoured jello follow the instructions on the package. For a 25g package bring 2 cups of water to boil, add the jello powder and stir so it does not stick to the pan. In 2 other pans do the same to the other flavoured jellos. Once the jellos are dissolved turn off the heat and add 2 cups of cold water to each jello.
Pour each flavoured jello into a rectangular mold/tupperware to a height of 1 or 2cm (depending on the size of squares you want in your jello) and let it cool in the fridge for a few hours until the jellos are solid.
To prepare the milk jello, in a bowl stir in the unflavoured jello in 1/2 cup of very cold water and let it hydrate and turn solid.
Add 1/2 cup of very hot water to the solid jello and gently stir the jello until it turns liquid.
To make the milk jello, in a pot add the condensed milk, evaporated milk, milk and vanilla extract. Add the melted natural jello to the pot and mix thoroughly at low heat. Once it's mixed well turn off the heat and let it cool down to room temperature.
Cut the flavoured jellos into equal squares. In a bowl mix all the squares so the colours are equally distributed.
Pour the flavoured jello squares into a jello mold and cover it with the milk jello. Put the jello mold into the fridge until the jello is hard.