A bit of thought on the flavor of a prison based world. I really like the flavor of white being facist and obsessed with maintaining the status quo. That shows the extreme of white's love of laws and order and even villifies it a bit, which I think is good for white. However, this would lead to designing cards that focus on stopping players from doing things, grinding things to a halt.
A problem I encountered when trying to design an Iconic white rare for a prison is that I wanted to make a creature who's job it was to keep the other player from doing things. It makes sense flavorfully and mechanically, but if all of white is supposed to be based around this, it might make games stagnant. I would like help finding a way to make white more proactive in this setting.
Considering this is Prison World, I'd imagine white would get a mix of Boros-esque enforcers and Azorious-like jailers.
We did have one at some point - look up The Labyrinth. The main issue was that getting everyone through a decent number of rounds within a month was a nightmare. There's always been strong support for a rerun, but even with four hosts it was extremely taxing on all of us. We're still looking into ways to fix this, so feel free to propose an alternate system.