Spray a 9" x 13" baking dish with non-stick spray. Set aside.
Place the Rice Krispies in a large bowl. Set aside.
In a large saucepan, melt the butter over low heat. Add the marshmallows, pumpkin pie spice, vanilla extract, salt, and food coloring (if using) and stir until marshmallows are completely melted.
Remove saucepan from heat, add Rice Krispies cereal, and stir until well-coated.
Using a spatula sprayed with non-stick spray, gently press mixture into baking pan. Decorate with sprinkles (if using). Allow to cool completely before cutting into squares or into desired shapes with a cookie cutter. Store treats in an airtight container up to one week.
If you can find Jet-Puffed pumpkin spice marshmallows, these work great. Reduce pumpkin pie spice to just 1 teaspoon and omit food coloring.
If you don't have pumpkin pie spice, you can use 1 and ½ teaspoons ground cinnamon, ½ teaspoon ground ginger, and ½ teaspoon ground nutmeg.