Add the sugar, lime juice and 3/4 cup water to a small saucepan and bring to a boil, stirring until the sugar dissolves. Add the green food coloring, remove from the heat and let cool.
Into 2 chilled highball glasses, add to each glass: a few ice cubes and 2 ounces of the lime syrup. Divide the grenadine between the glasses, then top off each with club soda. Garnish with a lime wheel and maraschino cherries.