Make the cake: Preheat the oven to 400 degrees F. Lightly coat 5 rectangle pans with butter and dust with all-purpose flour.
Sift the cake flour, baking powder, and salt into a large mixing bowl. Beat in, with an electric mixer, the butter a heaping 1/4 tsp. at a time on low speed, until the mixture resembles coarse sand.
Beat in the sugar a tbsp at a time, until the mixture resembles fine damp sand. Beat in the eggs one at a time. Add the vanilla and milk, and beat on medium-high just until blended.
Divide the cake mix into 5 bowls, and add each of the different food colorings to each different bowl to achieve a vibrant color. Pour each bowl into each of the separately prepared pan and bake until a wooden skewer inserted in the center comes out clean — 30 to 35 minutes. Set aside and let cool.
Make the frosting: Using an electric beater, cream the cream cheese and butter together. Add the chili powder and cinnamon first, then add the salt, vanilla, and confectioners' sugar.
Finally, mix in the melted chocolate and blend until smooth. If additional thickening is needed, add more sifted confectioners' sugar, a little at a time, until a spreadable consistency is reached.
Assemble your cake: Put bottom layer of cake on pedastal, slather with a thin layer of frosting. Stack remaining cakes, alternating with a thin layer of frosting. Then frost top and sides of cake.