That is not a rainbow. If I remember correctly, it is some kind of energy barrier, there to prevent one from jumping ahead of the quest and bypassing some of the bad guys.
The Prisoner is like that. Very three-dimensional, lots of opportunities where clever players could find faster and more efficient ways through. Not so much any more, the developers have plugged them all up, at least so far as I know, but then I rarely know about shortcuts.
Now that I think about it, the Prisoner is one of the most-adjusted quests in the game. And not just plugging up shortcuts, although there was a lot of that, but also changing the nature of how it works. It used to be, if you fell off, you ended the quest. Everyone, even those who did not fall, found themselves outside the quest needing to start completely over.
This mechanic was unique and interesting, but it also punished the better players for bringing along anyone new, and discouraged grouping.
Now when you fall off, you appear underneath the quest in a special room containing a Charisma-eating spider. Which represents yet another adjustment: the Spider used to be much more fearsome than it is now. Facing the Spider alone used to be difficult; probably others in the quest were going to need to rescue you. But no longer, the Spider is now easy, and really so is the entire quest, much much easier than it has been in its various forms and perturbations.
Easier or not, it is still a very lovely quest. Very.
🙂 😀 🙂