Bake the cookies according to the Gingerbread Cookies recipe for 12–15 minutes. Let cool completely, about 30 minutes.
Spoon the icing into a paper cone or pastry bag with a ¼-inch (6-mm) plain round tip. Pipe the icing around the edge of each cookie to form a border. Pipe the icing into the middle of the cookie, letting it run to the edges of the border (see illustrations). Gently tap the cookie twice to settle the icing. Set the cookies aside to dry, at least 6 hours or up to overnight.
In a small bowl, combine the green food coloring and 1or 2drops orange extract. Using a clean small paintbrush, stir until the mixture forms a paste as thick as honey. Brush the mixture on a paper towel or a piece of parchment paper to test the darkness of the color. Using delicate strokes, paint diagonal lines of green on each cookie from the tip of the tree to the trunk, working from both sides of the cookie. Clean the brush. In another small bowl, combine the cocoa powder and 1 or 2 drops extract. Stir with the brush until a thick paste forms. Paint thin vertical lines on the trunk of each tree to simulate bark. Let the cookies dry completely, at least 1 hour.
Store the cookies in an airtight container, layered between sheets of parchment paper, at room temperature for up to 3 days.