Line two sheet pans with wax or parchment paper. Set aside.
Make Green puppy chow: Place 8 cups Chex in a large mixing bowl. Set aside.
In a microwave-safe bowl combine 18-oz almond bark and peanut butter. Microwave for 60 seconds and then remove and stir. Continue microwaving in 30 second increments, stirring each time, until completely melted and smooth. Stir in green food coloring until mixture is bright green.
Pour green almond bark mixture over cereal and gently fold until coated. Add powdered sugar and continue folding until cereal is evenly coated. (Note: You may need to gently stir this for up to 5 minutes. The powdered sugar needs to coat every piece of cereal and get slightly moist in order for the green to show through.)
Pour green cereal out in a single layer on one of the prepared sheet pans.
Make Gold puppy chow: Place 3 cups of Chex in a large mixing bowl.
Melt 6-oz almond bark in the microwave until smooth, stirring every 30 seconds. Pour over cereal and stir gently until cereal is evenly coated.
Spread cereal out over second prepared sheet pan. Sprinkle generously with sanding sugar or sprinkles, tipping the pan to try and get most of the surface and sides covered.
Let the cereal pieces cool completely, 30 minutes to an hour. (You can speed this along by transferring them to the fridge.)
Break the gold cereal apart. Combine the green and gold cereal.
Enjoy immediately or store in an airtight container at room temperature (for 5 days), in the refrigerator (for 2 weeks), or in the freezer (for 2 months).