The grey zone can contain Blabbers, in which they have a carcinogenous effect. They manifest as an unlocalized crackling vibration similar to that of auditory emission equipment receiving static.
All space not occupied by matter in the grey zone is occupied by Sucklers. These cause the slow bioform degeneration also known as "aging".
The grey zone is known to be harvested by at least one group of interest. The Burgrr consortium periodically reaps large amounts of the population, manifesting as a facsimile of nourishment providers.
The "Suckler" may be responsible for the phenomenon of "dark energy" in the Grey Zone.
One theory I've always subscribed to is that there are other, "higher" zones that resemble the grey-zone. The (human) inhabitants of these zones are more awake to the universe they're living in than grey-zoners, but are still unable to comprehend the full perception range. Back when we used to do more role-playing in the comments, I RP'd as a fictional version of myself from the "blue zone", and I think there's one that's semi-canon called the "para-violet" or something like that... -- George Parkins