Combine the butter, cream cheese, pumpkin, sweetened condensed milk, and pumpkin pie spice in a skillet over medium heat. Stir constantly until thickened and well-combined. Stir in the graham crackers and white chocolate chips until melted and smooth. Add a few drops of food coloring if desired.

Continue to stir until the pumpkin cheesecake mixture releases from the sides and bottoms of the pan when stirred. (If in doubt, cook a bit longer-- it's better to be thicker than too thin.)

Pour over a butter-greased baking sheet. Spread into an even layer and refrigerate until firm, about 2 hours, or overnight.