When coming up with this, I realized that themes of decay, a mysterious character with strange powers but dressed in rags, and distant decaying landscapes all parallel very closely to the mythos of the King in Yellow. I'm not trying to go Lovecraftian - that would be at odds with the genre, and not particularly fun to play anyway - but I did like Chambers' original book, and a few of the things that have built on it. I thought perhaps the realm of the fetid equilibrium might lie among the Hyades and contain Carcosa, which would mean that on a substantial breakthrough of power, Sepiatone might become Doomed, with the King as his Nemesis. But that's a future thing anyway, we'll see what other possibilities crop up. Right now, the only references to that mythos are minor and aesthetic: Black stars and a pallid mask.
For a more immediate advancement, small things like getting a knife to stab people while they're weakened instead of just decking them, or non-combat things like getting a place to call home, would also be big benefits.
In a more medium term, powers could evolve in vague quantitative ways like letting them operate faster or cover larger areas, or in a few qualitative ways, like unlocking permanent changes.
Has Sam ever accidently broken something or hurt someone due to his power negation?
I'm thinking maybe not. His powers only weaken rather than damage, so it's difficult to imagine this scenario, and even weakening something at an inopportune time is a bit out there since his powers are difficult to use in the first place and making them too unbound would kind of be edging into the Nova's wheelhouse. But mostly, I haven't thought of a good little story along these lines.
I guess I'm actually kind of taking a liberty by making it able to weaken things and facilitate entropy/decay in a general sense, since "power negation" is presumably just meant to be about super powers - I think it's fine since although that increases his ability's versatility, every other change I've made to his power weakens them substantially in ease of use (and, for the illusions, in versatility) in ways that can be molded to the needs of the narrative. But it's still subject to GM thumbs up/down.
Does the overlay stay in place, or move with him?
It stays in place. He can make and spread or intensify it, and can use it for the illusions, but it's not connected to him and he has no real control over it.
It sounds like he creates a sepia overlay, that then itself drains the area of even mundane powers.
Exactly.
Does this overlay require concentration to stay, fade with time, or stay forever as a blight upon the land?
It fades away over time, and everything that it drained returns. Like the creation of the overlay zone and the draining of the powers, all this takes time. Different amounts of time though, creating it is slow at the scale of time that combat happens on, and probably requires unleashing to achieve meaningful results fast enough, but for it to fade should at least be until the end of the scene. Making permanent zones like this would be more the sort of ability to become available during play than during character creation, in part simply because it's a qualitative powerup that makes sense in the context of his original powers, and in part because that's an ability which substantially alters the world, and I reckon gaining the ability to meaningfully affect the world is a big part of the transition from childhood to adulthood that is included in the theming of this game.
What family does your character have?
Sam has visited his mother briefly after leaving. She acted happy of course, but that was it. He didn't stay long. He hasn't known his father since he was very young, and has no siblings. His maternal grandfather and aunt are still alive, but he hasn't seen them in a long time either.
Do you go to school?
Nah. Not worth it.
Do you have a secret identity?
A secret identity? I guess so. Where Sam Walters is and how to find him isn't a matter of public record, and he doesn't intend to introduce himself by that name either. It's a lot simpler to not mention unnecessary life details after all. But it's not like a huge secret or a double life or anything.