The triple terrace extends behind the Hall of Supreme Harmony, supporting two other halls behind the first: the small square Hall of Middle Harmony:
and the larger Hall of Preserving Harmony:
These are both throne rooms too. You might say, "He already has the Hall of Supreme Harmony for a throne room. Even an emperor has only one bottom - how can he use three throne rooms?" Well, the Emperors were more ingenious than you or me. They used the Hall of Middle Harmony to practice their lines before speeches and ceremonies, and for a place they could kick back before the real ceremonies got under way. The Hall of Preserving Harmony doubled as a feast hall, an exam room (the very highest stage of the literary examination system that was the entree to political life was held here) and also as a rehearsal area for bigger rites and an imperial changing room. At CJ Banks, I have to make do with sixteen square feet and a three-way mirror that shows my backside, but I guess the Emperor had bigger clothes to contend with so he needed room to spread out.
If you climb the terrace you can see the thrones in both halls. Dad decided to stay at ground level, but I walked up the terrace to the "Middle" hall. In passing, I got a good look at the dragon drainspouts:
The thrones are very similar: imperial yellow in color
and set in front of a red-edged gray background. Given that every single thing about the Forbidden City has been six deep in symbolism and meaning, there's probably some significance to the gray backdrop. However, I have no idea what it might be!
With all this harmony, there oughta be a barbershop quartet around here someplace...