Beat the butter with an electric mixer until smooth. Add the vanilla extract and pumpkin pie spice. Then add the confectioner’s sugar one cup at a time, beating with each addition.
Divide the buttercream into bowls to dye it. Place ½ cup of buttercream into a bowl and dye it a mossy green, using green food coloring and few drops of yellow and brown food coloring. Place it into a piping bag and cut a notch into the end, creating a DIY leaf piping tip.
Divide the remaining buttercream evenly into 6 bowls. Dye them the following:
Cream = leave as is (the spices in the buttercream will make it a warm, cream color)
Yellow = 3 drops yellow food coloring, one drop of orange food coloring
Orange = 2 orange food coloring, 2-3 drops of yellow food coloring
Red = 3 drops crimson food coloring, 1 drop yellow food coloring
Purple = 1 drop blue food coloring, 1 drop pink food coloring, 3 drops crimson food coloring
Brown = 3 drops brown food coloring, 1 drop crimson food coloring, 1 drop orange food coloring
Place the buttercream into piping bags fitted with Russian flower piping tips.