Combine sugar, 2 1/4 c. water and 3/4 tsp. salt in saucepan; heat to boiling.
Mix cornstarch and 1/2 c. water to make a smooth paste; add to boiling mixture gradually, stirring constantly; cook until thick and clear.
Remove from heat.
Combine egg yolks (if using) and lemon juice; stir into thickened mixture.
Return to heat and cook, stirring constantly until mixture bubbles again.
Remove from heat.
Stir in butter and lemon zest and food coloring.
Cover and cool until lukewarm.
For meringue, I prefer to use an * Italian Meringue because it resists weeping better (recipe below), but if you want the still delicious traditional meringue given with this recipe, then: Add 1/2 tsp salt to egg whites; beat until frothy.
Gradually add 3/4 c. sugar, beating until glossy peaks are formed.
Stir 3 rounded Tablespoons of either kind of meringue into lukewarm filling.
Pour filling into cool pie shell.
Pile remaining meringue on top and spread lightly over filling, spreading clear to every edge of crust so no filling or gaps can be seen (this helps with shrinkage and weeping).
Broil topping to brown tips of meringue.
Bake at 325° F. about 15 minutes or until lightly browned.
Cool on rack at least 1 hour before cutting. Chill.
