SIFT together the almond flour, pistachio flour and powdered sugar in a bowl and set aside. Discard any lumps in the sifter, do not force through (tip: your almond flour and pistachio flour should be as dry as possible, you may need to spread out on a baking sheet and allow it to dry for 1-2 hours).
Put room temperature egg whites in a mixer and whisk from slow to medium speed until foamy.
Add cream of tartar and continue to whisk until you have soft peaks.
Add your food coloring and vanilla and continue to mix until the color is mixed in. Continue to whisk until you have stiff peaks.
SIFT the flour and sugar mixer into the egg whites and discard any lumps.
Fold just until everything is combined. I use a silicone spatula that works very well. Press batter into the sides of the bowl to get out some of the air to avoid hollow macarons. The mixture will be sticky and should have a lava-like consistency, meaning when you pour it onto its self it sinks back into the batter with no lines after about a minute.
Put the batter in a pastry bag or macaron dispenser like this one on Amazon. Try to get all the air out of the bag before you start and then pipe with the bag straight up, you'll figure out what works best for you. I don't use a stencil which is why my macarons are not all the exact same size, but they are pretty close. Of course, you can use a stencil if you would like to.
Tap the pan on the countertop, you might see bubbles come up and that's what you want. You can also carefully poke bubbles with a toothpick before allowing the skin to develop. Let the pans sit for 30 minutes and do not touch or tap anymore or you will get cracks. Make sure the macaron shells are dry before baking or your macarons won’t have nice feet. You can test by touching the top lightly, nothing should come off on your finger and the should feel "dry".
Preheat oven to 325°F and line baking sheets with parchment paper or a silicone mat.
Bake for 10 minutes, one pan at a time, and rotate after 5 minutes. Let them rest on the pan for 10 minutes and then transfer to wire rack. Once cooled, make your favorite filling, place filling around the edge of one half of a cookie and place the second half gently on top. Be careful not to push too hard or you will smash your beautiful creation. Enjoy!