Line a 9x13 inch baking dish with parchment paper or coat with cooking spray. Set aside.
In a large saucepan, melt butter over medium heat. Once melted, add in all but 1 cup of the marshmallows. Reduce heat to low and continue stirring until completely melted.
Remove from heat and stir in the vanilla and salt. Add the cereal and the remaining 1 cup of marshmallows and gently stir until combined.
Pour into the prepared baking dish. Press gently with your fingertips just until completely spread out.
Allow to set at room temperature, about 1 hour. Cut into rectangles.
Decorating the Rice Treats
Line baking sheet with parchment paper. Cut your set treats into rectangles.
Add 1 cup of white candy melts and 2 tablespoons of vegetable shortening in a glass bowl. Microwave 1 minute at 50% power. Carefully remove from microwave and stir. Put back in microwave for 30 seconds at 50% power and stir. Repeat for 15 second intervals at 50% power until fully melted and a smooth texture.
At a diagonal, dip half of the rice treat into mixture allowing excess to drip off and place on your baking sheet. Repeat for each treat. Place baking sheet in refrigerator for 5 minutes to set the melted chocolate.
While white melts are setting, repeat the melting process for the red melts.
At a diagonal, dip half of previously dipped treat into red mixture allowing excess to drip off and place on parchment paper lined baking pan. There should be a band of white chocolate showing. Repeat for each treat. Place baking sheet in refrigerator for 5 minutes to set the melted chocolate.
While red chocolate is setting, repeat the melting process for the green melts using the remaining shortening. Pour melted chocolate into piping bag and carefully cut off tip of bag.
Drizzle the green chocolate over the red edge. Sprinkle on the crushed candy canes. Allow chocolate to set for 5 minutes in the refrigerator. Remove from the fridge and store at room temperature.
Notes
Kellogg's Rice Krispies cereal is not gluten-free and they no longer make the gluten-free version. I like the Millville rice cereal from Aldi. It is gluten-free and close in texture. You can use any GF cereal brand you like check the labels for malt and barley, neither are safe for celiacs or those on a gluten-free diet. Do not use puffed rice cereal.
Most brands of chocolate candy melts are gluten-free but check the bag to be sure. I used Wilton brand which labels all common allergens.
You can also color white chocolate using gel food coloring. Only add a tiny bit as food coloring can cause chocolate to seize up.