In a food processor or blender, pulse the almond flour and powdered sugar a few times until fine. Do not over pulse. Sift into a bowl with the salt.
In another bowl, beat the egg whites with a hand or stand mixer until frothy. Continue beating while slowly adding the granulated sugar and seeds scraped from the vanilla bean (or vanilla bean paste) until stiff peaks form. If using food coloring, add 2-3 drops after the vanilla.
Gently fold the beaten egg whites into the ground almond and powdered sugar mixture until combined, but be careful not to overmix. It should be the consistency of “molten lava” but not runny, about 40-65 folds.
Transfer the batter to a piping bag fitted with a 0.4 inch (10 millimeter) circular tip.
On a parchment lined baking sheet, pipe 1 1/2 inch (4 centimeter) circles at least 2 inches (5 centimeters) apart. Repeat with remaining baking sheets. If your oven runs hot, place an empty baking sheet under each baking sheet with the macarons to offer some protection against the heat.
Firmly tap the baking sheets against the counter to remove excess bubbles. If desired, top with a few rainbow nonpareils. Allow to rest uncovered at room temperature 30-60 minutes to form a shell.
Preheat oven to 300˚F (150˚C).
Bake the macarons in the center of the preheated oven until the tops become firm, about 15 minutes.
Allow to cool to room temperature before removing from baking sheet.