Heat oven to 450°F. Bake pie crust as directed on box for One-Crust Baked Shell, using 9-inch glass pie plate. Cool completely on cooling rack, about 15 minutes.
Meanwhile, in 2-quart saucepan, mix water and cornstarch; add sugar and corn syrup. Cook, stirring constantly, until mixture boils and slightly thickens. Remove from heat; stir in gelatin and food color. Cool completely in refrigerator, about 30 minutes, stirring occasionally.
Mix in blackberries. Spread in baked shell. Refrigerate until set, about 3 hours. Serve pie with topping and extra blackberries. Cover and refrigerate any remaining pie.