In a small mixing bowl, add cold water. Sprinkle the gelatin powder over the water and soak the powder for 2 minutes.
Add lime jello to the bowl
Add the sugar
Pour the hot water into the bowl.
Whisk until everything is dissolved.
Add lime juice, sour mix, tequila and liqueur. Stir to combine. For virgin shots, leave out tequila and liqueur.
Add food coloring if desired.
Pour remaining lime juice into a shallow dish. Pour salt into a similar dish. Dip the rim of each cup into the lime juice and the into the salt.
Pour the mixture into the cups, filling them 3/4 full. Refrigerate until set, which is between 60-90 minutes.
When you are ready to serve the shots, remove from the fridge and top with a small lime wedge.