In a medium saucepan combine sugar, cornstarch and salt. Pour the water into the cornstarch mixture and stir together over medium heat until it starts to boil. Continue stirring for about one minute; mixture should be thick and clear in color. Remove from heat and set aside to cool.
Mix together the apple, banana, pineapple and pecans in a medium bowl. Combine fruit with cooked mixture, adding food coloring and fruit preserver; pour into graham cracker crust. Cover and refrigerate for about an hour. Serve with whipped topping; garnish with chopped pecans if desired.