Preheat your oven to 350℉ and line a baking dish with parchment paper. In a large bowl, mix together ½ cup crushed graham crackers, ⅓ cup white sugar, 1 cup all-purpose flour, and ½ cup melted butter until well combined. Press this mixture firmly into the bottom of the parchment-lined pan and bake for 15 minutes. While the crust is baking, whisk together 2 cups sweetened condensed milk, 1 cup full-fat coconut milk, ½ cup sour cream, ¾ cup lime juice, and 2 tablespoons lime zest in a separate large bowl. If desired, add coconut extract and green food coloring, then stir until smooth. Pour this mixture over the pre-baked crust and return to the oven for an additional 15 minutes. Remove from the oven and immediately sprinkle 1 cup sweetened shredded coconut over the top while it’s still warm. Refrigerate the bars for at least 2 hours to allow the filling to set. When ready, lift the bars out using the parchment paper, slice, and serve.