Place frozen limeade concentrate in a blender along with the seltzer, lime juice, food coloring (if using) and vodka (if using).
Pulse blender a few times to blend ingredients and its the consistency of a slushy.
Pour into glasses and top with the Italian ice.
Makes 2 generous servings.
Notes
Plain seltzer may be used if you prefer to use cherry-lime syrup. Use about 1/4 cup of the syrup to start and add more as desired.Nutrition calculated without the vodka.