There are many mysteries and questions that Dragon Ball fans have about aspects of the series that are never really clarified. Where did Vegeta's pink "Bad Man" shirt come from? Why did the Heeters wait so long to implement their plan to take over Freiza's empire? Why does Yamcha fail at everything he does? The world may never know.
One fan has taken to Quora to ask one of the more profound questions: Why is Broly's energy green? Broly is a Legendary Super Saiyan, who is said to only appear once every thousand years. Because of the threat he posed, King Vegeta had him stranded on planet Vampa with his father until they were found by the Freiza Force later on. We see hints of green on Broly's outfit in the form of a green pelt around his waist, but we learn that is from a fallen friend rather than his Great Ape form. The color coordination between his armor does not explain his unique green aura though. In contrast, the other Super Saiyans all usually have yellow or gold auras unless using a different type of energy, such as Super Saiyan Blue. Sometimes, Goku will have a red aura, especially in the older episodes.
The answer as to why Broly's aura is green lies within Dragon Ball Super: Broly. As Quora user Rui Silva aptly explains, in the movie, we're told that Broly's power "works kinda in reverse to that of a normal Saiyajin." They then link to a gif that shows Vegeta going Super Saiyan and just for a moment, we see his hair turn green before going to turning to the iconic blonde. Furthermore, Broly's hair does turn blonde during the fight with Gogeta, but his aura is green. By the end of the fight, though, Broly was using his Ikari, or Wrathful, energy. This is the main difference between his power and the powers of Goku and Vegeta. In the Wrath State, Broly can draw on the power of the Great Ape form while still in his human form. It's when Broly draws on this more primal power that his hair turns from blonde to green.
Following this explanation, Broly's energy goes from yellow to green rather than the standard green to yellow. While the green-to-yellow aspect of going Super Saiyan was never really talked about before the movie, Toriyama has played around with the idea of different levels to the Super Saiyan form, which is why there are so many variants of it now. As of writing, the Dragon Ball Super: Broly's version of the character is the one considered canon since that story falls within the timeline of the show. The 1993 Dragon Ball Z: Broly-The Legendary Super Saiyan version of Broly wasn't considered canon, though fans did respond positively to the character. This version of Broly would receive a trilogy where, in the final movie, he would be cloned. The Broly clone, also known as Drooly, could also draw on the same power as Broly Prime, but because he was unstable, he mutated when trying to reach the Legendary Super Saiyan form.
