House of Stone?
I've been thinking about this for a long time now and I was wondering if anyone else did too. What if the Kell's Guard is part of the House of Stone? They have no banner coloration which either means, they have no House or maybe Stone's color was Grey as stone is often depicted as being grey, and if you die to them no House is listed. Perhaps after the Whirlwind occurred the House of Stone was wiped out and the survivors began to roam in packs and serve whomever pays them enough akin to Taniks, the Scared. That or they're all together and when The Guardian came to assassinate Draksis, they wiped out the remaining Stone survivors. Virgil the Ghost