Make the lime layer: Coat a 6-cup bundt pan lightly with cooking spray. Mix the cold water and gelatin in a small bowl and gradually sprinkle the gelatin evenly on top; let bloom 5 minutes. Combine the limeade concentrate and sugar in a medium saucepan over medium-low heat. Cook, stirring, just until the sugar is dissolved, 2 to 3 minutes. Remove from the heat and stir in the bloomed gelatin until it is completely dissolved. Stir in the food coloring to make a vibrant green color.

Strain the lime gelatin and pour into the bundt pan. Let cool until just warm, then refrigerate until the gelatin is just set, about 4 hours.

Meanwhile, make the eggnog layer: Put the milk in a small bowl and gradually sprinkle the gelatin evenly on top; let bloom 5 minutes. Combine the heavy cream, sugar, allspice berries and nutmeg in a medium saucepan over medium-low heat. Cook, stirring, until just hot and the sugar is dissolved, 2 to 3 minutes. Remove from the heat and stir in the vanilla bean paste and bloomed gelatin until the gelatin completely dissolves. Let cool to room temperature, about 1 hour. Strain into a spouted measuring cup.

Once the lime layer is set, pour the eggnog mixture slowly and gently over the top. Refrigerate until firmly set, 8 hours or overnight.

To unmold, dip the pan in very warm water, about 15 seconds. Invert the pan onto a plate and give it a shake; you should hear a plop. If not, dip in water again for a few seconds and repeat until the gelatin easily comes out in one piece.