Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

In a large bowl, cream the cold unsalted butter and granulated sugar until fluffy and light, about 3-4 minutes.

Add the large egg to the mixture and mix on low speed until fully incorporated.

In a separate bowl, whisk the all-purpose flour, baking powder, and salt together. Gradually add to the butter mixture and mix on low speed until a soft dough forms.

Divide the dough into 3-4 parts and add 1-2 tablespoons of Jello powder to each, mixing until the dough is evenly colored.

Wrap each section of dough in plastic wrap and refrigerate for 15-20 minutes.

Roll small balls of dough (about 1 inch) and coat them in additional sugar before slightly flattening and placing on baking sheets.

Bake for 8-10 minutes until edges are set; they should appear slightly crackled.

Cool on the baking sheets for about 2 minutes before transferring to a wire rack.