Dragon Ball Super: Broly has shaken the foundation of the entire foundation not only because it introduces Broly and Gogeta into the series' official canon, but because of all the potential for future stories it introduces.
One potential theory has caught fans' attention as it suggests that a "Super Saiyan Green" transformation may be on the way.
Warning! Major spoilers for Dragon Ball Super: Broly below!
When Vegeta's battle with Broly reaches a new level, Vegeta transforms into a Super Saiyan. But before he transforms, his hair turns into a strange green color. It's not like Broly's green aura, but it's more like a Seafoam green that's shown for a moment before Vegeta's successful Super Saiyan transformation. As theorized by Geekdom 101 and Kendamu on YouTube (which you can find at this link), this particular green is so pronounced that it may be Vegeta tapping into the same kind of power that Broly uses.
Before Broly transforms into a Super Saiyan in the film, there's a mid-tier transformation in which he taps into the power of the Saiyans' Great Ape form. Without his tail, he's allowed to gain this power and still keep him humanoid form, and this results in his green aura. Vegeta's brief green hair moment could be a subtle hint that Vegeta has this latent power as well.
There's another moment that seems to emphasize this further when Goku transforms into Super Saiyan Blue for the first time. When pushing beyond Super Saiyan God, his aura turns green like Broly's. It eventually leads to Super Saiyan Blue, but this color was noticeable and too pronounced to completely ignore. Now the film itself pushes a lot of boundaries in terms of how the franchise has been animated, and thus plays with its color palette.
These strange asides to "Super Saiyan Green" will most likely be just another way Dragon Ball Super: Broly plays with its art. But on the other hand, Dragon Ball has seen Super Saiyans with yellow hair, pink hair, red hair, blue hair, silver hair, and green hair. There may very well be a "Super Saiyan Green" down the line before we know it. Maybe even as the canon version of Super Saiyan 4?
Dragon Ball Super: Broly is now open in theaters worldwide, and has already gone on to have a bigger lifetime gross than Dragonball: Evolution. Funimation brought the film to the United States on January 16, and tickets for the film are now on sale. You can read ComicBook.com's spoiler-free review of the film here, and Dragon Ball Super: Broly is described as such:
"A planet destroyed, a powerful race reduced to nothing. After the devastation of Planet Vegeta, three Saiyans were scattered among the stars, destined for different fates. While two found a home on Earth, the third was raised with a burning desire for vengeance and developed an unbelievable power. And the time for revenge has come. Destinies collide in a battle that will shake the universe to its very core! Goku is back to training hard so he can face the most powerful foes the universes have to offer, and Vegeta is keeping up right beside him. But when they suddenly find themselves against an unknown Saiyan, they discover a terrible, destructive force. Locked into battle with the formidable Broly, Goku and Vegeta face their most dangerous opponent yet!"