Potentium

The Potentium is a view of the Force. Counter to millenia of teaching, the followers of Potentium claimed that there was no light side or dark side, just the Unifying Force. They claimed that what others called the light side was actually just the Force itself, which is inherently good. What others called the dark side was a preversion of the Force, twisted by those who used it. The light and dark sides were in the user, not the Force. They also said that the Jedi Masters refused to believe it because that would mean that the Jedi were not needed to fight evil, for evil did not exist. A century before the Battle of Naboo, the followers of Potentium were expelled (unviolently) from the Jedi Order. Yoda and the rest of the Jedi Council did not consider them Darksiders, but they said it was the duty of the Jedi to use the Force to protect others, not study it's absolute limits. The Council said that testing the Force to its limits would lead to the dark side.

Followers
The exact date Potentium was theorized is lost to history, though it appears to have had some followers as early as the Old Sith Wars. Jolee Bindo could be considered one of the first, since he saw "more gray than dark or light." Kreia also believed in Potentium, as she trained her students as Grey Jedi. Sekot, the intelligence of Zonama Sekot, accepted Potenium after it's awakening, when it was colonized by some of the outcast followers. The Colonists felt Zonama Sekot was proof of the Potentium, and Sekot eventually came to consider itself the protector of the Force (self appointed as some derisively point out). Vergere, an Old Republic Jedi who was captured by the Yuuzhan Vong, also believed in Potentium. Due to her influence, members of the New Jedi Order such as Luke Skywalker, Mara Jade Skywalker, Jacen Solo, etc. adopted the Potentium as the truth of the Force. Some outside the order (and even within) feared the Jedi had grown blind to the dark side.

Surprisingly, Emperor Palpatine also appeared to be a follower of the Potentium, as he didn't teach Darth Maul in terms of light or dark side. He also revealed to Anakin Skywalker that there is only one Force--the difference was that the Sith saw it as a means to an end, while the Jedi saw it as an end itself. It is unknown if this is Palpatine's own personal view of the Force, or outright Sith Doctrine.