In a mixing bowl, add in the graham cracker crumbs, sugar and butter. Stir until it looks like wet sand.
Press the graham crackers into an 8 inch pie plate.
Place in the oven and bake for 12 minutes. Set aside to cool while you make the filling.
Filling
In a large mixing bowl, add in the sweetened condensed milk and food color if you chose to use it. Since the condensed milk is thick, it will help easily mix the food coloring in.
Add in yolks and grapefruit juice. Stir by hand until combined. Do not whisk or form bubbles.
Pour into the graham cracker crust.
Place in the oven at 350 and bake for 30 minutes or until the center is set.
Let cool and place in the fridge for 3 hours to overnight to finish setting up.