I found this graphic of the Sith, Jedi and Grey Codes. Very cool! The more I think about it, the more think that Luke is a Grey Jedi. The book with what looks like the Grey Jedi symbol, the talk of balance and something bigger, the talk of ending the Jedi, and the fact that Luke is wearing grey.
First off, that graphic is fan made. Secondly, it's use of those symbols are somewhat misleading. All three are canon, but the one in the middle is not the symbol of the "Grey Jedi" (since there's no such thing, but more on that later) it is
the symbol of the Jedi Order. The one on the right is in fact the symbol of the Old Republic. As in the Republic that fell to the Sith Empire(s?) before the whole Darth Bane and the Rule of Two thing and, obviously before the Republic featured in the prequels was founded. Or re-founded/restored/reformed, depending on how one views such things.
I won't mince words about the next bit since the trailer seems to have been giving people some ill informed ideas: "Grey Jedi" aren't a thing. It was something that was kicked around in the EU, mostly in the DH comics and a little in KotOR. The concept has no basis in anything GL has ever said or depicted and by all accounts, the current thinking at LF is that there ain't no such thing and there never was.
The idea of a Jedi that can use the dark side without consequence is anathema (to say nothing of pure fanwank.) It's like saying someone is a "tolerant Nazi" or a "carnivorous vegetarian". It's a contradiction in terms and stems mostly I think from a persistent misconception that the dark/light dichotomy of the Force is a simple "good vs. evil", "life vs death", "yin vs yang", and by extension a misunderstanding of what the concept of "the balance of the force" even means.
I've explained this once recently already this week, but I'll do so again: the dark side is not just another way to use the force, it's an aberrant perversion of the natural order. It's what happens when your take the natural give-and-take cycle of the Living Force & the Cosmic Force and bend it to your will, *causing* an imbalance. It's cancerous and insidious and toxic. There's no middle ground a Jedi can walk and still call themselves a Jedi.
Now this is not to say that there aren't other doctrines that view the force differently than the Jedi (there are!) nor that there can't be Jedi who leave the order and go there own way (there have been!) or even that there can't be some doctrinal schism within the order itself (there's been at least two that we know of!) But none of this has resulted in an individual or organisation with the appellation "Grey Jedi".
Ahsoka was not a Grey Jedi. She was a Jedi who left the order. After that, she was just Ahsoka.
Qui-Gon Jinn was not a Grey Jedi, he was a Master in the Jedi Order who was prone to disobeying the council. That doesn't in and of itself make him a special kind of Jedi. His ideas were more about a Jedi's relationship to the living and cosmic force. He did not propose that Jedi should use both the dark and light, because that would be preposterous.
Put simply: a Jedi that rejects the teachings of the Jedi is no longer a Jedi. QED. As I said, this has happened in canon. Typically said Jedi becomes a Sith, as was the case with Vader & Tyranus, though there's obviously more to it than that. Ventress trod a similar path, but she was never really a Sith and come to that, she was never a Jedi either. Her training was incomplete and it's implied her Master took her on without so much as informing the council (apparently even more of a maverick than Qui-Gon, but still not a "Grey Jedi" I'm afraid.)
The first of the two big examples is of course the Sith Order, who's founder believed (like some fans it seems) that the Dark Side was just another aspect of the force and one the council was foolishly ignoring. The council disagreed and expelled him from the order. So no longer a Jedi and certainly not "Grey".
The second is the
Ordu Aspectu, which is something just recently added to canon and inspired by
an old Marvel comic strip from way back, written as it happens by some obscure snake god worshipping comic book writer I'm sure nobody has heard of.
Unlike the Sith (whom they may or may not predate: it's not clear), this splinter sect tried to make some sort of an accord with their former brethren Jedi, but what they were poking around with ultimately backfired and they were all (mostly) destroyed, lost and all but forgotten.
