Line a small baking sheet with aluminum foil and fold to make a “mini” pan that’s about half or a quarter of the baking sheet. Spray with nonstick cooking spray.
Spray the inside of a saucepan with nonstick cooking spray. Add 1 tablespoon butter and melt over medium heat. Stir in 1 cup marshmallows and 1 tablespoon Jello and/or some food coloring, if desired. Cook, stirring, until marshmallows are melted.
Turn off the heat. Add 1½ cups rice krispies and fold together until combined. Transfer the first color of rice krispies to the prepared pan.
Run your hands under cold water. Gently press the rice krispies down into the pan to create your first layer.
Repeat steps 2 through 4 to create as many color layers are you’d like!
Cut the layered rice krispies treat into 1-inch slices. Arrange a few slices at a time on a baking sheet covered with foil and nonstick cooking spray. Warm in a 300˚F oven until soft and moldable.
Remove from the over and bend into a rainbow shape; set aside to cool.
Melt 1 tablespoon butter and 1 cup marshmallows in a clean saucepan until melted. Spoon the melted marshmallows over the bottom of the rainbows and use it as “glue” to attach mini marshmallow clouds.