3 (12 ounce) cans frozen limeade concentrate, thawed
12 fluid ounces vodka
1 drop green food coloring, or as desired (optional)
1 (2 liter) bottle lemon-lime soda (such as 7-Up®), divided
Mix limeade concentrate with vodka, green food coloring, and 1 1/2 liters of lemon-lime soda in a large plastic container with a lid. Cover the container and freeze the mixture for 1 to 3 days. Scoop the frozen slush into glasses and add a splash of the remaining lemon-lime soda to each glass.