I always like looking at older Toy Fair catalogs as they tend to have many preproduction items shown. The Detention Block Rescue playset was no exception. The toy shown appears to be an early conceptual design made from Kenner's model shop.
When comparing it to the production playset, it is almost a complete redesign including the blue double blaster cannon, turrets, floor, walls, etc.
The cannon is not only in blue, but an entirely different sculpt. The green missiles would've been much cooler!
The production box art shows the same unreleased playset, but with the newer sculpt laser cannon in blue.