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Place it in the refrigerator for at least 20 minutes. Remove it when the top is just starting to set and leaves a tight edge against the side of the pan. Try a sour cream layer for a big contrast. Place the gelatin in the refrigerator again for at least 20 minutes to let the second layer set. Spoon in the next layer and refrigerate for at least 20 minutes. Repeat spooning and refrigerating until you have used the last of your Jello mixtures.

Summary:
Spray the metal or silicone mold with cooking spray. Pour one mixed bowl of gelatin into the bottom of your pan or mold. Spoon the next color onto the top of the last color. Remove the gelatin mold. Place it in the refrigerator to set overnight.