Immediately after the apocalypse, a call went out for able-bodied adults in what was considered a noble death sentence at the time: go out into the radioactive wastes and begin to neutralize the fallout. Those that volunteered were provided radsuits, the means to repair said radsuits indefinitely, and lumbering zamboni-like machines that tilled the top six inches of soil under the ground so as to effectively bury the radioactive dust that had settled, then applied a thin layer of bacteria-synthesized Prussian Blue to the turned earth to serve as both a marker of 'neutralized' ground and to provide protection against caesium created by uranium-235.
Two hundred years later, this group still exists in the wastelands, having multiplied and flourished in their nomadic journeys. They have essentially become a cargo cult, still fulfilling their purpose in the 'blue zone' and essentially elevating the lumbering cleaning machines (along with their self-sustaining bacteria tanks) into supernatural protectors while they await the return of those who gifted them these great earthmovers.
I'm trying to think of a good, scientific reason to give them an odd physical trait that disallows easy reintegration into society. Originally, I hoped the Prussian blue was an effective skin dye, but I haven't yet figured out a way to pull that off without giving them major potassium deficiencies. They're likely a bit inbred by now, so my second thought was something akin to methemoglobinemia, the inherited disease that makes people's skin turn silvery. But combine that with the radiation they must have absorbed in their lifetimes, it strains credibility to say they managed to wander a radioactive zone for generations with a blood disease.
Can you think of a good, easily-discernible physical difference this group might have that would help reinforce their isolation without resorting to Fallout-style ghouls/supermutants (overdone) or crippling diseases?
I can come up with plenty of ideas story-wise, but I'm coming to you guys for science-based, rational consequences of the scenario I've set up.