Refrigerate 10 champagne flutes or cocktail glasses until chilled. In a small bowl, combine corn syrup and green food coloring; dip rims of chilled glasses into mixture. Turn glasses upright, allowing mixture to slightly run down sides of glasses. Freeze until firm.
In a pitcher, combine the pineapple juice, grape juice and yellow food coloring if desired. Refrigerate until chilled.
Just before serving, stir club soda into juice mixture. Pour juice into prepared glasses; garnish with pineapple if desired.