Blend together the confectioners’ sugar and almond flour in a food processor and sift into a large bowl.
Make a French meringue with the egg whites and granulated sugar, making sure to add about 10 percent of the sugar at the start of whipping. When making the meringue, gradually add the sugar in several additions, and add the food coloring a little bit at a time as the mixer whips on medium speed. Add enough coloring to obtain a deep color purple. Whip until just under stiff peak.
Fold the meringue into the dry ingredients, making sure that the batter has no lumps and is smooth, but not runny. If under-mixed, the surface of the macaron will be lumpy. If overmixed, the macaron batter will run too much after piping and will not hold a round shape.
Line 2 very flat sheet pans with silicone paper or a nonstick rubber mat. Using a #5 straight tip, pipe a circle with a diameter of about 5cm / 2 in. The batter should run slightly, just enough so that the surface is smooth.
Let the macarons dry, uncovered, for at least 30 minutes. This is what gives them their characteristic look. While they dry, preheat a deck oven to 225°C / 440°F.
Bake the macarons in the back of the deck oven, where it is hottest, for about 6 minutes with the vent open. Pull to the front of the oven for 1 to 2 minutes longer to keep a close eye on the macarons to make sure that the structure of the macarons sets. Make sure that the insides of the macarons are not too wet, otherwise they will fall and lose their volume after being taken out of the oven. They also may be underbaked to the point where they do not lift off of the silicone paper.
Let the macarons cool completely on the sheet pan before removing and filling.
Reserve in an airtight container or in the freezer for up to 1 month.