01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking soda, baking powder, and salt in a medium bowl. Set aside.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, about 2 minutes.
04 - Add egg and vanilla extract, beating until well combined.
05 - Gradually add dry ingredients to wet ingredients, mixing until just combined.
06 - Divide dough evenly into two bowls. Add one flavor of Jello powder to each bowl (about 3 tablespoons per bowl) and knead until color and flavor are incorporated.
07 - Scoop tablespoon-sized portions, roll into balls, then gently roll in extra granulated sugar.
08 - Place cookies 2 inches apart on prepared baking sheets.
09 - Bake for 8–10 minutes until edges are set but centers look slightly underbaked for chewiness.
10 - Let cookies cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.