Empty the contents of the red and green gelatin into two separate sauce pans. Pour 400ml of water into each pan. Stir to dissolve the gelatin granules. Cook over medium heat, stirring often, just until the mixtures start to bubble. Pour into two separate trays and allow to cool and set.
When the green and red gelatin have set, cut into one-inch cubes. Pour into the mold. Stir lightly to distribute.
Empty the contents of the two packs of unflavored gelatin into a clean sauce pan. Place the cream in a measuring cup and add enough water to measure 800ml. Pour into the sauce pan, stirring to dissolve the gelatin. Cook over medium heat, stirring, just until the mixture starts to bubble.
Pour the white gelatin into the mold. Do this little by little so that each time you pour, a few of the red and green cubes float. That way, the red and green cubes are distributed rather than remaining at the bottom.
Cool and chill the gelatin for a couple of hours before serving.