Combine the powdered sugar and almond meal in a bowl and mix together thoroughly with a whisk or fork. Pass through a medium-coarse sieve to lighten and aerate the mixture (which makes it easier to fold).
In a glass measure, add enough egg whites to reach halfway between the 1/3 cup and 1/2 cup mark; or use a scale to weigh out 3.75 oz. of egg whites. Transfer these to a large bowl, and save the rest for another purpose or discard. With an electric mixer, beat the egg whites at medium speed until they form soft peaks when the beaters are lifted; add the almond extract and the coloring, if using. Beat at high speed until the mixture forms stiff but not dry peaks when the beaters are lifted. Pour all of the almond flour mixture over the egg whites. With a large rubber spatula, fold the almond mixture into the egg whites just until it is fully incorporated. The egg whites will deflate somewhat, but the batter will be thick and moist and almost pourable.
Drop heaping teaspoons of batter 1 inch apart on parchment-lined cookie sheets. Or transfer the batter to a large pastry bag fitted with a 1/2-inch plain tip and pipe out disks in the following manner: Hold the bag vertical with the tip about 3/8 inch from the pan liner. Squeeze the bag without moving it until a disk of batter 1 1/2 inches in diameter is formed. Stop squeezing a second or two before moving the bag to pipe the next disk. Repeat, piping disks 1 inch apart. Let the macarons rest for 20 to 30 minutes, or until the surface of the disks is ever so slightly dry-this slightly dry crust will help form characteristic little "platforms" at the base of each macaron as they bake.
Meanwhile, preheat the oven to 400°F. Position racks in the upper and lower thirds of the oven.
Slide two sheets of macarons into the oven and immediately turn the temperature down to 300°F. Bake for 12 to 15 minutes, until the macarons are barely starting to turn golden (they will be golden on the bottom, though you will have to destroy one macaron to find out). Rotate the pans from top to bottom and from front to back halfway through the baking time to ensure even baking. Set the pans or just the liners on racks to cool.
When the cookies are cool, lift a corner of the parchment pan liner. Holding a cookie with the other hand, carefully peel the liner away from the cookie (don't try to pull the cookie off the liner or you will lose the bottom of the cookie). Repeat with the remaining cookies.
Spread 1/2 to 1 tsp. filling on the flat side of a cookie and top with a cookie of matching size. Put the cookies on a tray and cover them with plastic wrap. Put the trays in the refrigerator to let the cookies mellow at least overnight and for up to 2 days before serving. Bring to room temperature for serving.