Preheat your oven to 350°F (175°C). Prepare an 11x7 inch baking dish by greasing or lining it with parchment paper.

In a food processor, combine all-purpose flour, powdered sugar, and salt with cold butter. Pulse until it resembles coarse crumbs. Press into the prepared baking dish and bake for 18–20 minutes, until golden brown.

While the crust is baking, whisk together granulated sugar and a bit of flour in a medium bowl. Add eggs one at a time, mixing well. Stir in grapefruit zest and juice. If desired, mix in pink food coloring.

Pour the grapefruit filling over the warm crust. Bake for an additional 20 minutes, until the edges are lightly browned and the filling is set.

Allow the bars to cool in the pan for about an hour, then refrigerate for at least 2 hours before slicing.