Preheat your oven to 350 degrees F. Line a baking sheet with a silicone baking mat or parchment paper. Set aside.
In a large mixing bowl, beat together the cake mix, egg, Cool Whip, and vanilla. The dough will be thick and sticky.
Divide the cookie dough evenly between two bowls (I use the mixing bowl as one of them). Add a couple of drops of red food coloring to one bowl and mix until combined. Add more food coloring as needed to reach your desired color. Repeat using the green food coloring and the other bowl of cookie dough.
Put the powdered sugar into a small bowl. Use a 1-tablespoon cookie scoop to portion the dough directly into the bowl of sugar. Roll it around until it's completely coated. Place the ball onto the prepared baking sheet. Repeat with the remaining cookie dough. Leave 2 inches between each cookie. (Seriously, the cookies spread A LOT. You'll need to work in batches.)
Bake for 12 to 15 minutes or until the cookies are set. The center of the cookie will still be soft. That's okay.
Remove from the oven and let the cookies cool on the baking sheet for 5-10 minutes. Carefully transfer the cookies to a wire rack to cool completely.