Lime Layer: Mix 3/4 cup water and the lime gelatin in a medium-sized mixing bowl. Whisk until combined. Add half of the key lime yogurt container and whisk again. Pour mixture into a medium-sized sauce pan. Sprinkle 2 1/2 tablespoons (or 1 envelope) of unflavored powered gelatin on top and let sit for 1 minute to activate. Whisk until combined.