Spray a 9 x 13 dish with non-stick spray and set aside.
Add 5 cups of mini marshmallows and 3 tablespoons of butter in a large microwave-safe mixing bowl. Microwave for one minute, stir with a rubber spatula, and then microwave in 30-second increments until smooth (I usually only need to do this one more time).
Add 5+ drops of blue food coloring, 1 teaspoon of vanilla extract, and ¼ teaspoon of salt, and stir until the mixture is a cohesive blue color.
Add 4 cups of rice krispies cereal to the blue marshmallow mixture and gently mix until all the cereal is coated making sure to scrape along the sides of the bowl.
Add the mix to the 9 x 13 baking dish. Lightly spray your hands with non-stick spray and use them to gently press the rice krispies into an even layer.
Repeat with a clean bowl and no food coloring, but add 1 cup mini marshmallows to mix in with the rice krispie cereal.
Repeat for a third layer with red food coloring.
Let the rice krispie treats sit to harden for about 1 ½ hours or as needed. Once firm enough, spray a knife with nonstick spray to cut the rice krispies into 12 equal rectangles.