Combine hot water and sugar in a large measuring cup. Whisk until all sugar is dissolved. Pour into a pitcher (at least ½ gallon capacity).
Add the cold water, lemon juice, and lime juice. Stir until combined.
Start with a toothpick of green gel food coloring (it is very concentrated). Add it to your lemonade and stir well. Keep adding coloring until desired color is reached.
Refrigerate until cold. Garnish with lime slices, if desired.
Notes
Adapted from the Food Network
Recipe by Not Your Momma’s Cookie at https://notyourmommascookie.com/2012/08/wicked-green-elixir/