Wash and dry the limes. Cut each lime in half and squeeze all the juice out. Reserve 1 tablespoon of the lime juice and store the remaining juice, covered, in the refrigerator to use for another time. Turn the lime halves inside out to easily peel or scoop out the pulpy insides and set aside.
Add the water to a medium saucepan, sprinkle the gelatin over the water and let it sit for a few minutes until it dissolves.
Heat the water over low heat and stir until the gelatin has fully dissolved, about 3 minutes. Remove from the heat and stir in the limeade concentrate and fresh lime juice. Allow to cool down a little more and then add the tequila.
**Optional: To make the lime jello a green color, add 1 drop of green food coloring to the liquid mixture at this time and mix well.
Place the lime shell halves on a plate and evenly pour the mixture into them, being careful not to tip them over. Cover and place in the refrigerate until set, about 4 hours.
To serve: Remove the jello limes from the refrigerator and cut in half. Sprinkle with the salt and serve immediately. CHEERS!
**Consume the jello shots within a 24 hour period because the white pith inside the lime shells will make the jelly taste bitter if left in too long. Adapted from a recipe by Baked Bree