Line a baking sheet with parchment paper or silicon mat(aff. link).
Sift together the almond flour and powdered sugar. If you can't find almond flour you can always make it with almonds and a food processor. Finely grind the almonds and sift through a fine mesh sifter. Discard or snack on any large pieces.
In a large mixing bowl, add in egg whites. Turn on high and beat until the egg whites form a soft peak meringue.
Add in the granulated sugar, salt, vanilla extract, and cream of tartar. Mix on high until a stiff peak meringue forms. I slowly but constantly add in the granulated sugar into the meringue instead of tossing it all in at once.
Add in the sky blue gel paste color and give it a quick mix to incorporate.
Very lightly and carefully fold in a third of the almond flour/powdered sugar into the meringue with a spatula. Repeat with the rest of the almond flour/powdered sugar mixture. All together you'll want to have about 59 turns of this mixture. If you don't mix enough the macaron shell will be extremely fluffy and cracked. If you over mix, the macaron shell will be extremely flat and might not form a foot.
Preheat oven to 300 degrees.
Fill a piping bag with the macaron shell filling. I just used a coupler on the end of my piping bag. Pipe macaron shells on the baking sheet.
Let the macarons dry until they are no longer tacky to the touch. It will take 20 minutes to 1 hour.
Place in the oven for about 10 minutes until they no longer stick to the parchment paper.
Let the macaron shells cool.
Once the macarons are completely cooled, add the vanilla and brown in a small bowl. Stir to combine.
Using a brand new paint brush and a plastic glove, dip the brush in the brown and flick the brush against the glove to begin adding speckles. Just a warning, put an apron on because you can't really control where the food coloring goes.
Once you're content with the speckles, set aside to drive. It took mine about an hour or two to dry.
In a mixing bowl, add in all of the frosting ingredients. Mix on low until incorporated. Turn hand mixer on high and beat for 1 minute until fluffy.
Add the frosting in the piping bag with a straight tip.
Add a thin and even layer of frosting on the bottom macaron. Add the top macaron and twist to squish the frosting out slightly. Repeat with all macarons.