[@sundered echo] can answer the reason blindness can be difficult. 

The quota of grey Jedi at this point is filled.

As for teetering on the edge is something we are a bit uncertain about, but we wouldn't want to restrict you to a pure lightsider. That would just be boring. 

The reason we would discourage someone from being right on the edge of falling to the dark side is simple: the Sith respect strength. Someone falling easily would feel weak to them. 

But the older a Jedi, the more illustrious his/her history of fighting the Sith, the closer he or she could theoretically be to that edge of falling. Of course, beyond a certain point, it would become implausible. And at this stage we do not want any Jedi masters among the prisoners. 

But a senior Jedi who has slowly begun to approach a 'ends justify the means' mentality following nearly three decades of war could fit well. Especially if he or she is somewhat blind to how close to the edge (s)he is.

Of course, you could always go with a younger one close to falling, but that one would be considerably less likely to survive. 

We are also very fond of flaws. Take note of the above and write up a concept, and we can see how well it will fit, [@Kal-El].