Whilst I once previously roleplayed a Shade myself, I was altogether against the circlejerk that happened for years upon years due to the existence of the Shade Gems. This seems mostly ok.
There isn't really much I can suggest here for improvement, aside from clarifying on the whole new "Tsperkn zu'Serthekhur", as well as the link of Shade to Moz Strimoza. This could just as easily be put under a new name and not be associated with the old Shade, as none of it's origin has anything to do with what the previous origin was, under Arun'Asna, etc, all that **** in the past.
I think you'd be able to accomplish much better RP in not at all linking this to the old Shade, instead stating Shade as a simple inspiration, and elaborating and creating your own origin, or perhaps a shift-over, an explanation for why this returned, after such an extended death. Those few who actually seek to roleplay Shade for the downside aesthetics, as I once had [though I've since moved on entirely from this lore in general, after having been the one to shoot it in the head in the end] who take it up once more, or anyone who does actually choose to take this up, should be aware it's clearly more of a downside feat with some added aesthetic to magic if you do have any magic.
Whilst it's good on the aesthetics front, I don't really think there's any need for a Shade Gem at all, as it really just led to hierarchies - which I don't see this as something that should have a hierarchy at all. I also suggest you go more indepth into the nature of the Parasite itself, including it in this piece, etc.
This is something I don't see merit in, alongside the Shade Gem and the unexplained origin. I think it could be something that could be possibly abused, and should be an ability outright listed along the two others, with proper emote counts and whatnot listed, as well as limitations and such, to prevent it from being abused.
All in all, I think you should really elaborate more on the downsides of the feat, beyond the redlines and what's seen of it in the lore itself. It's not so much a Magic as it is a simple, antagonistic curse, of a far weaker level than it had originally been, that is capable of imbuing certain aesthetic properties unto other magics. I'm not against this at all, but like I said, I encourage you to not link it to the old Shade, as it seems to have a mix of unexplained origin and some history from a couple maps back when Tsuyose had the magic. When it comes to picking one or another out of the 2 origins, I'd go for the former - elaborate on this unexplained origin, cut off the old origin, as the two mix like oil and water. I think it'd make it more appealing to explore for anyone who does bear this curse - emphasis on curse.