In small saucepan, combine raspberries and cornstarch; cook and stir until thickened and clear. Cool 10 minutes. Chill thoroughly, about 20 minutes.
In large bowl, combine sweetened condensed milk, lemon juice and food coloring if desired. Fold in whipped cream. Spread one-third lemon mixture into prepared pastry shell; top with raspberry mixture then remaining lemon mixture.
Chill thoroughly. Garnish as desired. Refrigerate leftovers.