Steel was released on the second series of Hasbro's JLA line, right alongside Martian Manhunter, which may mean they were in production for Kenner's Total Justice at the same time. If so, that may be why they were on the same mission in the coloring book.
Interestingly, the art of Steel does not match the figure that was eventually released: that one was an original mold, with his S symbol merely painted on the chest; this design, with no symbol, shield-shaped clasps for the cape, and tubes running down the outside of the legs, looks like nothing so much as the Deluxe "Blast Hammer" Steel from the 1995 Man of Steel toyline. Since the only "armor" he seems to wear in any of the art is an extra eyepiece that would have slipped over the head, it's possible he had simply been chosen for a spot in Total Justice, but hadn't been designed yet, or that Kenner felt that old sculpt was dynamic enough to be reused with minimal new tooling.
That may also be why all he does in the story is scan Mars to find out where the piece of the Ultimate Weapon is, tunnel through the ground, and then get knocked out of the fight by Darkseid before J'onn and Kyle show up.
