Nutrition per serving may change if servings are adjusted.
3 cups limeade, divided
1/8 teaspoon spirulina, dissolved (see Tip)
1 cup cold water
4 envelopes unflavored gelatin
1/3 cup sugar
2 cups diced mixed citrus, such as orange, lime and/or grapefruit
Bring 2 cups limeade to a boil in a small saucepan over high heat.
Meanwhile, pour water into a large heatproof bowl. Sprinkle gelatin over the water; let stand for 3 minutes. Add the dissolved spirulina to the remaining 1 cup limeade and stir to completely dissolve the gelatin, 2 to 3 minutes. Add sugar and stir for 1 minute to dissolve.
Refrigerate until the mixture is the consistency of thin pudding and is just starting to set around the edges, 1 to 1 3/4 hours. The time will vary depending on the size of your bowl and how cold your refrigerator is. After 1 hour, start checking every 5 to 10 minutes because it thickens quickly after that.
Gently but thoroughly whisk the mixture until it's uniform. Stir in diced citrus. Pour into a 9-by-13-inch pan. Cover the pan with plastic wrap, without touching the jello.
Refrigerate until very firm, about 3 hours. To test if it's ready, touch it with your finger. If your finger does not stick, it's done.
Run a small, sharp knife around the edge of the pan. Cut into 16 squares then gently pry the squares out with a butter knife.
Make Ahead Tip: Refrigerate for up to 3 days; unmold just before serving.
Tip: Spirulina—dark green edible plankton—is sold in powdered form (bulk or in capsules) near vitamins and supplements. Once dissolved in water, it can be used in place of artificial food dye to add dark green color naturally to things like homemade jello desserts. To dissolve spirulina, place 1/8 teaspoon in a 2-cup glass measure. Slowly stir 2 tablespoons very warm water into the spirulina. Continue stirring until it's completely dissolved, then add 1 cup cold limeade. Proceed with recipe as written. Add more dissolved spirulina, if desired, for a darker green color.
54 calories;0 g fat(0 g sat); 0 g fiber; 13 g carbohydrates; 2 g protein; 6 mcg folate; 0 mg cholesterol; 12 g sugars; 10 g added sugars; 37 IU vitamin A; 10 mg vitamin C; 9 mg calcium; 0 mg iron; 6 mg sodium; 35 mg potassium