Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, baking soda, and salt.
In a large bowl, cream the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.
Beat in the egg and vanilla extract until well combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Divide the dough into two equal portions.
Add half of the dough to a separate bowl and mix in the Jello powder until fully incorporated.
Scoop tablespoon-sized portions of the Jello dough and plain dough, and roll them together to form a ball.
Roll each ball in powdered sugar and place them on the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10-12 minutes or until the edges are lightly golden.
Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.