Okay so basically once you reach the facility
(it’ll be after the puzzles with yellow laser walls which block supra balls from passing)
you’ll want to turn to your right once inside and there will be a stone wall with a hidden entrance.
Walk along the wall to find the path and you’ll see 3 pink rings (rings and switches can only be activated by their associated color) along with a paint machine and some stones. Simply drop your pink cube into the paint to switch the paint color to pink and paint a stone pink.
The stone is small enough to drop through the rings and the chest containing a red moon is yours!