Pulse together the almond flour and powdered sugar in a food processor.

Add 2 egg whites to the almond mixture and process until smooth, resembling almond paste.

Add food coloring of your choice and continue processing until the color is evenly blended.

Transfer the mixture to a large bowl and set aside.

Combine water and sugar in a saucepan and cook until a candy thermometer reads 110°C, about 15 minutes.

Beat 2 egg whites until soft peaks form using an electric mixer.

Gradually pour the hot syrup into the meringue while beating until stiff peaks form and the mixture cools.

Gently fold 1/4 of the meringue into the almond mixture with a spatula.

Fold in remaining meringue until fully incorporated.

Pipe batter onto parchment-lined baking sheets.

Allow to dry at room temperature for 1 hour.

Preheat oven to 275°F.

Bake for 20 minutes, rotating sheets halfway through.

Prepare lemon buttercream filling while macarons cool.

Remove macarons from oven and transfer to cooling rack; leave on parchment.

Once cooled, pipe buttercream onto the flat side of one macaron and top with another.

Store completed macarons in an airtight container in the refrigerator for 24 hours before serving.