For the cake pops: Line a baking sheet with parchment paper and set aside. Combine the cake crumbs and frosting in a large bowl. Work the frosting into the crumbs with your hands until it forms a thick paste and can be easily rolled into balls.
Roll the mixture into 12 balls and place on the prepared baking sheet. Freeze until almost solid, 20 to 30 minutes.
For the decoration: When ready to decorate, melt the white chocolate discs in a double boiler and keep warm. Melt the red and black chocolate discs in small bowls in the microwave. Remove the cake pop balls from the freezer and insert a plastic or metal fork into each. Dip the tines of another fork into the red chocolate and wave over the bowl of white chocolate to make flecks and drizzles. Insert cake pops into the white chocolate and swirl to coat completely. Let any excess drip off, then place a green chocolate disc in the center to form the iris of the eye. Set down on the prepared baking sheet and allow to set while you repeat with the remaining cake balls. Dip the back of a skewer into the black chocolate and make a large dot in the center of the green on each pop. Clean the skewer, dip into the white and make a small dot to the side of the black. Allow to set completely at cool room temperature or in the refrigerator until ready to serve.
In the bowl of a stand mixer fitted with the whisk attachment, combine the confectioners' sugar, butter, milk, vanilla and salt, and whip on low speed until incorporated. Turn the speed up to high and whip until the buttercream is smooth, scraping down the sides of the bowl once or twice. If it's too wet, add a bit more confectioners' sugar. If it's too stiff, add a bit more butter.
Use immediately, or store in an airtight container at room temperature for 24 hours or in the fridge for up to 2 weeks. Rewhip cold buttercream before using it.