Preheat oven to 350 degrees. Grease or spray a 9x13" pan. First prepare the crust. In the bowl of your food processor, mix 2 cups flour, butter, 1/3 cup sugar, salt, and 1 tsp. vanilla, until fully combined, and crumbly. Press firmly into the bottom of the pan, and bake for 15 minutes. Meanwhile, get the filling started. In a medium bowl, whisk eggs, remaining sugar and flour, lime juice and vanilla until fully combined. Add the food coloring, if desired. When the crust is done, remove and pour the filling onto the hot crust. Bake for 20 more minutes, remove and let cool completely. Cut into squares, and refrigerate for about 1 - 2 hours. Serve.