Before I dive in, I want to offer a quick note on spelling. I've seen a good deal of discussion about this topic on various social media platforms, with a mix of grey vs gray being used. Neither is incorrect, as far as I'm concerned. Gray is the more common spelling in American English, while grey is the more common spelling in British English. But you're going to find both versions in this article, depending on who's being quoted. So, here's to hoping it doesn't bug you too much.
Why all the interest in Grey Jedi?
While Grey Jedi are largely a Legends (non-canon) concept at the moment, there are at least a few hints that they might become part of canon in the near future. In the recent High Republic (formerly, Project Luminous) announcement, there is a shot of Star Wars author Justina Ireland standing in front of a whiteboard with creative concept ideas. Right at the top, you can see "Grey Jedi" written out and circled. Just underneath that line, you can also see "Splinter group of force users" written and circled.
It isn't addressed in the video at all, but the vast majority of the circled concepts on the whiteboards became part of the Lucasfilm narrative for the High Republic era. So this may be a concept they've decided to include in their storytelling, without formally addressing it in the announcement (they have to have some surprises to reveal).
I would also suggest that the sequel trilogy lends further credence to the idea. Rey was not truly a Jedi and Kylo was not truly a Sith. These Orders, are something akin to a religious practice that neither Rey nor Kylo seemed keen to adopt in perpetuity. Rey ultimately did harness both sides of the Force, if only briefly; and Kylo does the same when he lays his hands on Rey.
I use the sequel trilogy as a directional cue only because it's recent, and several of the Lucasfilm Story Group members that worked on the trilogy's development were present at the Project Luminous summit in the aforementioned video. Nonetheless, we've seen Anakin and Luke harness anger and hate when facing their enemies. While Anakin ultimately succumbs to the Dark side, Luke does not. But both appear to tap into the Dark side of the Force as Jedi, however briefly it might be. Not to mention, Anakin returns as a Force ghost after Vader's demise - an ability that generally seems limited to Light side users within canon.
While this isn't meant to be an all-inclusive list of canon examples, I would be remiss if I didn't mention Jedi Master Mace Windu. The Vaapad style of lightsaber combat he perfected was built around the concept of channeling one's inner darkness in a controlled manner. It's a form that was controversial from its inception, because it ostensibly violated the Jedi tenets against passion and chaos. Although Master Windu may have perfected the style in a way that satisfied the Council, it still stands as a canon example of a prominent Jedi harnessing their dark impulses without succumbing to the Dark side of the Force.
What does Lucasfilm say?
Not much. Any formal reference to Grey Jedi in Star Wars publications has been relegated to Legends (non-canon). While the aforementioned examples may support the idea that a Force adept can teeter that line - at least for a time - they are not formally referred to as Grey Jedi. Likewise, we've seen Jedi leave the Order, in canon, without ever turning to the Dark side. But they are not formally referred to as Grey Jedi, either.
About a week prior to the High Republic announcement, Lucasfilm Story Group Executive, Matt Martin, was asked about the canonical status of "Grey Jedi" on Twitter. While he confirms they are not canon, his response was ambiguous enough to be left to interpretation. And the Star Wars fandom certainly has devised wildly different interpretations of that response.
The most obvious ambiguity lies in the qualifier he used: without consequence. Does that mean a Force user could tap into powers from both sides with consequence? And what might those consequences be? The corruptive nature of the Dark side - in terms of the physical, mental and spiritual toll it can take on a person - is fairly well covered within canon sources. Are these the consequences he speaks of? A Jedi that is slowly losing his mind, perhaps even suffering from physical deformities, is not necessarily lost to the Dark side. So wouldn't that fit the mold of a Grey Jedi, even if it's only for a time?
Why the controversy?
You've probably come across an image like the one below, which attempts to delineate between Jedi, Grey Jedi and Sith using their "codes." The problem is, there is no such thing as a Grey Jedi code in current canon, and there's not even a strong consensus within Legends publications. One might ask themselves why a Force wielder that rejects the strict tenets of the Jedi and Sith would have an established code at all. A personal code based on individual moral principles - sure. But that could have wildly different underpinnings from one character to another, so it doesn't lend itself very well to a matter-of-fact comparison like this one.
Before I jump into the opposing positions, there's a tertiary issue raised by reader Duncan Truthwaite that bears a brief discussion. There are some fans that only oppose the use of the word Jedi in describing these ambiguous Force wielders. The reasoning behind this stance is that the Jedi Order is akin to a religion and anyone that refuses to follow its code, or willfully leaves the Order, is no longer a Jedi of any sort. Therefore, you shouldn't call them Grey Jedi - maybe Grey Adepts, or something along those lines.
From what I can gather, there seem to be three major opposing positions concerning the introduction of "Grey Jedi" into canon:
1. A Force user can either harness the Light or Dark side of the Force. They cannot straddle the two.
In most cases, Force users do remain firmly grounded on one side of the Force. And when someone turns to the Dark side, it is most often a permanent endeavor. But the more interesting Force wielding protagonists and antagonists within canon don't necessarily adhere to a strictly black and white connection with the force, as I've noted in several examples above. So while a black and white interpretation might well describe most Force adepts in the Star Wars universe, I don't see that as a hard rule within current canon.
2. Grey Jedi refers to a Light side Force user that ignores or subverts the strict tenets of the Jedi Order - it doesn't mean they can harness the powers of the Dark side.
We've seen Jedi in canon that subvert the will of the Jedi Order (e.g. Qui-gon Jinn), or decide to leave the Order entirely (e.g. Ahsoka Tano), without ever succumbing to the Dark side of the Force. It seems reasonable to refer to these Force wielders as Grey Jedi. They do still morally align with the Jedi Order, even if they don't fully adhere to their strict beliefs.
The "Splinter group of force users" concept I mentioned from the Project Luminous summit might be a way to play on that idea. At the height of the Jedi Order, there were thousands of Jedi in the Galaxy. It's reasonable to assume that a handful of them may want to leave the Order for similar reasons. And they could end up banding together to fulfill whatever tasks they believe are necessary to maintain balance in the Force. This doesn't seem like a stretch by any means.
3. Grey Jedi walk the line between the Light and Dark side of the Force, allowing them to harness powers from both.
As some fans have rightfully pointed out, a Force wielder that can harness Light and Dark side powers without consequence would be incredibly boring (and potentially overpowered). But I don't see any reason that these stories would need to unfold in such a mundane fashion. A character like this would likely experience considerable struggle in controlling emotions like fear, anger and hate, while simultaneously trying to use them to channel the Force. Pushing their powers too far could cause them great pain, mental anguish, physical deformities, or perhaps even drive them mad.
Internal conflicts aside, any Force practitioner that overtly tried to walk that line would almost surely be treated as a threat by the Jedi Order, even if they remained generally aligned with them from a moral perspective. They may be forced to face the Jedi - maybe kill another Jedi - even though they have no direct quarrel with them.
This, too, could play into the aforementioned "splinter group" concept. Walking the line between Light and Dark could be an incredibly precarious and taxing experience. It may be a venture better attempted with a support group of like-minded Force adepts. You would no doubt have those that would succumb to the ways of the Dark side in such a group, and others that would be too reserved to push the boundaries any further. That kind of setting is ripe for various types of conflict; and by proxy, some incredibly interesting story arcs.
This is all just one Geek's opinion, of course. Where do you stand on the issue of Grey Jedi? Do you hope the concept is formally introduced into canon? How would you handle it if you were the decision maker at Lucasfilm? Let us know in the comments or on social media!