Prepare a 9x13 inch baking dish by greasing it with cooking spray.
In a large saucepan, melt the butter over low heat. Add the mini marshmallows and stir until completely melted and smooth.
Remove the saucepan from heat and stir in the vanilla extract.
Gradually add the Rice Krispies cereal to the marshmallow mixture, stirring until well coated.
Divide the mixture into three equal parts. In one part, mix in the red sprinkles or melted red candy. In the second part, mix in the blue sprinkles or melted blue candy. Leave the third part plain.
Press the red mixture evenly into the bottom of the prepared baking dish. Follow with the plain mixture, pressing it down gently. Finally, add the blue mixture on top, pressing it down to create an even layer.
Allow the treats to cool completely at room temperature for about 30 minutes before cutting into squares.