For the Pickled Rind: Peel the green skin from the outside of the melon rinds. Trim any remaining flesh from the inside or overly tough rind from the outside. Slice remaining rind into 1/4-inch planks. Cut into small decorative shapes with a cookie cutter or knife. Combine water, vinegar, Kool-aid, and sugar in a medium saucepan and bring to a simmer. Add watermelon and simmer for 30 minutes. Strain rind out into a heat proof container and continue simmering liquid until it reduces by about a third, around ten minutes. Pour reduced liquid over rind and allow to cool to room temperature, then cover and chill at least 24 hours.