Line two 8x8-inch baking pans with parchment paper and spray with nonstick spray. Set aside.
Place ¼ cup of water in a small bowl and empty 1 envelope of unflavored gelatine over the water. Don’t stir! Let sit and “bloom” for 2 minutes. Then, you can stir and microwave for 10 seconds if necessary. Repeat with another ¼ cup of water and envelope unflavored gelatine, keeping them separate. Set aside for now.
2½ cups water, ½ ounce KNOX unflavored gelatine
In a microwave-safe bowl, heat the remaining 2 cups of water to boiling. Remove and divide into 2 small bowls, placing 1 cup of water in each.
Sprinkle the cherry Jell-O in one bowl of water and the lime on the other. Stir until the Jell-O has melted, then add 3 tablespoons of sugar to each bowl of Jell-O.
6 ounces cherry flavored Jell-O, 6 ounces lime flavored Jell-O, 6 tablespoons granulated sugar
Add one of the bowls of unflavored gelatine to the cherry Jell-O and stir until combined. Add a few drops of red food coloring if so desired. Pour into one of the prepared baking pans and place in the refrigerator. Repeat this step with the lime Jell-O and place it in the refrigerator once it is poured into the pan. Refrigerate until set hard--this may take 2 or more hours. You want these to get very jellied and dryer.
Red and green food coloring
Remove the pans and lift the parchment paper with the Jell-O out of the pan. Set on a hard surface and cut out shapes or cut into small cubes, using cookie cutters or a knife.
Place the coarse sugar in a bowl and roll each piece until coated.
1 cup coarse sugar
Place the gumdrops on a platter or parchment paper-lined baking sheet.
Store in the refrigerator until ready to serve.