below is a theory on why Xayah, Rakan, and Neeko all seem to wear green in their costumes, along with my hypothesized timeline.
Xayah, Rakan, and Neeko all wear GREEN upon their lapels and dressage, a color long often tied to the FIRST STAR. to wear such a color meant to be one with nature and the very primal essence that this being inhabits, a responsibility that now only a single guardian per team has the right to wear and thus communicate more directly with the being that observes them. however, Xayah, Rakan, and Neeko are guardians of a bygone era, all three of them beings from far beyond Valoran. this is a tentative timeline of what could be my take on the star guardian era, with time intervals in between each event being of flexible eras:
1. the first star and the present universe is born.
2. the first star creates beings out of cosmic material to serve under him.
3. the first star creates mortal beings to live among the universe, the first of them being the vastayasha’rei, all the way down to humans.
4. a group of the cosmic beings rebel against the first star in jealousy of these mortal beings, leading the first star to create the first wave of Star Guardians from the first mortal race he had created: the vastayasha’rei.
5. the cosmic beings are banished to the dark recesses of the known universe.
6. the first star, in preparation and prevention of another rebellious uprising, blesses certain mortals with star guardian powers, among them being humans. this second wave of star guardians are led by the vastayasha’rei, and among them they create a new race: the vastaya. out of these mortals, only vastayasha’rei and vastayas are allowed to done green due to being of or directly related to the first race.
7. ages pass and Neeko, one of the original wave of star guardians, leads a team of five: Rakan, Xayah, Zoe, and Ahri, with Ahri being the newest member among them.
8. Zoe, perhaps out of jealousy from her vastaya counterparts ( or, even, boredom ? ) and their ties to the First Star turns to look for another source of power, stumbling across the dark cosmic beings that were banished by the original star guardians.
9. Zoe turns away the First Star in favor of darker powers, and using her newfound ability she creates tears in the reality that imprisoned the dark stars … thus setting them loose once more upon the First Star’s creation.
10. Zoe furthermore finds her old teammates ( and the new member that replaced her, Sarah Fortune ) in her new form, succeeding in killing two of them, separating their pseudo-leader, and leaving Ahri and Sarah alone.
11. the First Star, seeing what his bias towards Vastayas has created, takes away the emerald power from the majority of his guardians, leaving only one member of each of his teams to wear the color and be the team’s collective representative in communication with the primal power.
12. Ahri and Sarah scout and receive new teammates from Earth, where they meet one of the newest guardian teams: Team Lux.
13. and now, we are at present day, with Neeko still on the run from Zoe’s corruption and Xayah and Rakan having succumbed to their revival with darker powers.
NOTE: Canonical Zoe is much older than most of the Vastayas, however i am keeping the fact that Star Guardian is very much its own separate universe from Canonical League so i have taken creative liberties.
again, this is all theoretical and something i have come up with in my own time! any feedback is welcome!