Place nonstick silicone baking mats or parchment paper sheets on several baking sheets. This recipe makes 100+ cookie shells, so you need several baking sheets. (See notes below.)
Weight the almond flour and powdered sugar with a food scale.
Place the almond flour, powdered sugar, and pumpkin pie spice into a food processor. Process on high speed until the mixture is fine.
Sift the flour mixture into a large bowl, discarding any large almond pieces, if necessary. Set this sifted mixture aside.
Using a mixing bowl and the whisk attachment, beat 6 egg whites until foamy. Add the cream of tartar and beat to dissolve it. Then add 1/3 of the granulated sugar and beat for a minute until the sugar dissolves. Add half of the remaining sugar and beat for an additional minute. Then add the rest of the sugar and beat until firm, glossy peaks form, a couple of minutes or more.
Add a little orange food coloring (if using). Beat on medium speed to mix. Add more coloring if desired to reach the desired orange color. Beat between each addition. Do not overbeat.
Gently fold the dry ingredients into the beaten egg whites. Fold with round circles around the bowl, scraping the bowl's bottom. Mix well in a folding motion. The batter will be thick.
Use a whisk or fork to beat the 1/2 egg white until frothy. Stir this egg into the batter to soften and moisten it.
Set up a pastry bag with a round tip. Then place it in a tall cup and fold the bag sides over the cup sides. (This will hold the pastry bag while you fill it with batter.) Add about half of the batter to the bag.
Pipe the batter onto a macaron mat. Hold the bag perpendicular to the mat and squeeze out a circle of batter about 1 to 1 1/4 inches in diameter. Space the cookie shells far enough apart so they can spread later.
As soon as the pan is full of cookies, tap the baking sheet firmly on the counter a few times to remove any air bubbles. This will spread out the batter a little. Do not wait too long to tap the baking sheet to prevent a skin from forming on the cookies before you are ready. Repeat until all the macarons are piped onto baking sheets.
Let the macarons dry out for 60 minutes to form a skin on top. Test by touching. If no batter sticks to your finger, they are ready to bake. If not, let them sit a little longer and test again.
Preheat the oven to 300°F. Bake the macarons for 14-15 minutes on the middle rack. Keep a check and do not let them brown, or they will lose their color and overcook.
Cool completely to prevent sticking. Then carefully remove the cookie shells from the mat.