Due to the nature of meringue - which is easily sabotaged by outside moisture -coloring macarons naturally to a deep hue is tricky. The best ingredients that color naturally are also common macaron flavors: cocoa powder in chocolate shells and ground pistachios, which create light green shells. Fair warning, however, that when it comes to cocoa powder, it is only replacing a small amount of the almond flour in any viable recipe (about 10%). Too much cocoa powder and you'll end up with cute, little brownies instead of French macarons. As for plant-based food coloring, widely available natural brands are much less intense than gel-based artificial ones. So in order to achieve a shade even half as bright, you need to use twice as much. And this will add too much moisture to the batter, which will cause the egg white proteins formed during the whipping to collapse. In other words, all your hard work whipping the whites can be undone in one fell swoop of a teeny, tiny bottle of food coloring. As previously noted, attempting to tint macaron shells with freeze-dried fruit and vegetable powders can cause similar problems like too much cocoa powder. The color may deepen, but the meringue will suffer and you can end up with splotchy, sunken, or cracked macarons. The best choices when it comes to coloring macarons are to proceed au natural as with vanilla bean or opt for a small amount (or sometimes more) of artificial gel food coloring.