Tangy Grapefruit Tart

Preheat oven to 400°F. Lightly brush crust with egg white. Bake for 5 minutes or until lightly browned; set aside to cool. In a medium saucepan stir together the sugar and cornstarch. Add the juice; cook and stir over medium heat until thickened and bubbly. Gradually whisk half of the mixture into the egg yolks. Return mixture to saucepan. Cook and stir constantly until mixture boils gently. Cook and stir for 2 minutes more. Remove from heat. Add butter and stir until melted. Stir in food coloring. Pour mixture into prepared crust. Cover loosely and chill for 4 to 6 hours or until set. Top with coconut and pistachios.