Preheat oven to 375°F. Take your 3 boxes of yellow cake mix and put into 3 separate bowls. Add 2 tsp. of peppermint Schnapps into each bowl, and then add 1 tsp. mint extract to each. Take your food coloring and add as little or as much as you want to get the color that you desire, make 2 red cakes and 1 green or 1 red and 2 green. Mix well with an electric mixer on medium or with a wooden spoon; make sure there are not lumps.
Spray 3 round pans with cooking spray with flour; then add your mix and make sure you don't over fill it, but fill it a little over half way. Bake according to box directions, and then let cool on a wire rack for 10 minutes.
Take your cakes out and just slightly cut the tops off leaving a smooth surface to work with. Then flip the cake over to where the bottom is now the top. Take your vanilla frosting and add a tsp. of mint extract. Cover the top of the bottom then add your middle cake. Cover the top of that and add your top cake, but be careful, at this time your cake will be very fragile, and then cover your whole cake. Now take a Ziploc bag and put as many peppermints as you like and crush them till there almost fine, with a rolling pin; sprinkle on top of cake and try to get some around the cake too, if you can, then garnish around the edges with peppermint patties.