On the audio commentary for the dvd release of this episode, Bruce Timm personally storyboarded the showdown between Superman and Darkseid, because he felt he knew these characters well enough, and he knew how much they despised each other, and it would only work properly if that energy and emotion was captured properly on paper first.
Superman's uniform was changed to black and grey by Darkseid's Omega Beams. This is the same look the actual Superman costume George Reeves wore had in Adventures of Superman (1952) while filming the black and white episodes in Seasons 1 and 2.
Last show of the series.