Preheat your air fryer to 350°F (175°C).

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until well combined.

In a large mixing bowl, cream together the softened butter and granulated sugar until the mixture is light and fluffy.

Beat in the egg, vanilla extract, and buttermilk until fully combined, ensuring no lumps remain.

Gradually add the dry flour mixture to the wet mixture, stirring until no streaks of flour remain.

Divide the dough into two portions. Mix blue gel food coloring into one portion and pink into the other until evenly distributed.

Using a cookie scoop, portion out marbled dollops of pink and blue dough into a single layer in the air fryer basket, leaving space between each cookie.

Air fry the cookies for about 10-12 minutes, or until the edges are lightly golden and the centers appear soft.

Allow the cookies to cool on the air fryer basket for a few minutes before transferring them to a wire rack to cool completely.