Heat 1/2 cup water to boiling in a medium-sized, heavy-bottomed saucepan.
Dissolve one packet of gelatin in the boiling water. If the gelatin is not pre-packaged in packets, one packet is equivalent to 1 tablespoon or 1/4 ounce.
Stir 1/2 cup of liquid soap or bubble bath and a few drops of food coloring into the mixture, whisking gently to combine. Do not beat the mixture; if it becomes foamy it will not set properly.
Pour the soap mixture into a clean jar or tray. Place in the refrigerator and cool until firmly set. To use, dissolve 1 to 2 ounces of jelly in a running bath or use directly as a cooling shower gel.