Preheat your oven to 350°F (175°C). Grease or line an 11x7-inch baking dish.

In a large mixing bowl, combine all-purpose flour, powdered sugar, and salt. Add room-temperature butter and blend until it resembles coarse crumbs. Press mixture into the bottom of the dish and bake for 18-20 minutes until golden brown.

While the crust is baking, whisk together granulated sugar and flour in a bowl. Add eggs one at a time, mixing thoroughly after each addition. Stir in grapefruit zest and juice. Optional: add pink food coloring.

Pour the grapefruit filling over the hot crust. Bake for an additional 20 minutes until filling is set and edges turn light golden.

Cool at room temperature for about 1 hour, then refrigerate for at least 2 hours before serving.