Preheat oven to 375 degrees. Lightly spray bottom only of a 9-inch spring form pan and set onto a baking sheet. For crust, combine graham cracker crumbs, melted butter and yogurt in a small bowl; press mixture evenly on bottom and 1/2 -inch up sides of prepared pan. For filling, in a large mixing bowl beat cream cheese, sugar, flour, and vanilla with an electric mixer until combined. Beat in milk just until smooth. Stir in egg substitute, lemon, lime and orange zest. Pour filling into crust-lined pan. Bake for 35 to 40 minutes or until a 2 1/2-inch area around the outside edge appears set when gently shaken. Meanwhile, prepare topping by combining sour cream, granulated sugar and lime juice in a small bowl. When cake is done, remove from oven and spoon topping over the cheesecake, spreading evenly. Return to oven and bake for an additional 5 minutes. Cool in pan on a wire rack for 15 minutes. Using a small sharp knife, loosen the crust from sides of pan; cool for 30 minutes more. Remove the sides of the pan; cool cheesecake completely on a wire rack. Cover and chill at least 4 hours before serving. Garnish with very thin slices of lemon, orange and lime.