Fresh basil turns a blackish color when exposed to heat which is why you may notice that the vibrant green color of your homemade basil pesto turns a much darker color by the time the filets are cooked.   Don’t worry - that’s a normal reaction and it won’t impact negatively on the taste of the filets, especially since I’ve only added 3 tablespoons of pesto on each side of the Tilapia. You can also serve the air fried Tilapia with additional fresh basil pesto too!