Bloom the gelatin: Pour the cold water into a medium bowl. Sprinkle all 4 packets of unflavored gelatin evenly over the surface. Let sit undisturbed for exactly 5 minutes until the gelatin has absorbed the water and looks thick and wrinkled. Do not stir yet.
Dissolve the gelatin: Pour boiling water (or hot juice) over the bloomed gelatin and whisk vigorously until completely dissolved, about 2 minutes. No lumps should remain. Add sugar now if using, and stir until fully dissolved. Divide the mixture evenly into two bowls.
Color Layer 1: Add 2-3 drops of your first gel food coloring to one bowl and stir well. Let the mixture cool to room temperature (about 15-20 minutes), then check the temperature, it should feel just slightly warm to the touch, around 80-85°F.
Pour Layer 1: Lightly grease your mold with non-stick spray. Pour the cooled Layer 1 mixture into the bottom of the mold. Refrigerate uncovered for 2-3 hours until the surface is tacky but not fully firm (it should jiggle but hold its shape and feel slightly sticky when touched lightly).
Prepare the cream layer: While Layer 1 is chilling, gently warm the heavy cream or coconut cream in a small saucepan over low heat until just steaming (do not boil). Add the remaining half of your dissolved gelatin mixture to the warmed cream and whisk until smooth. Add your second color (or leave white for contrast). Let cool to room temperature.
Pour Layer 2: Once Layer 1 is at the tacky stage, carefully pour the cream gelatin mixture on top. Pour slowly over the back of a spoon to prevent disturbing the first layer. Return to the refrigerator for at least 3-4 more hours, preferably overnight.
Unmold the trick: Fill a large bowl or your kitchen sink with warm (not hot) water, about 100°F. Dip the bottom of the mold into the warm water for exactly 8 seconds. Remove, run a thin flexible spatula or butter knife around the edge to break the seal, then place a chilled serving plate firmly on top. Flip quickly and confidently. Hold for 30 seconds without peeking. Lift the mold straight up slowly.
The reveal: Step back and admire your work! The layers should be perfectly distinct, with a gorgeous wobble and stunning color contrast. Serve immediately or refrigerate (covered) for up to 4 hours before serving.