Yellow lightsabers are the most underrated lightsaber color in Star Wars. They were used in the Old Republic video games and used by some of the strongest force users. They’re usually apart of the Sentinel faction of the Jedi who are the “protectors”. Unfortunately, this saber color hasn’t been used in the newer films or on screen at all (excluding Rebels) even though some Jedi on the Jedi council in the prequels had this color.
Most of these users didn’t stick around the Jedi temple but were usually off on long missions. The most well known user is Bastila Shan from the Knights of the Old Republic video game. She had a double bladed yellow saber. She was special only because she had the force ability called Battle Meditation which involved making those who fought against whoever she was fighting for, lose their courage to fight and those who fought with her to gain more courage. In some instances, those who wielded a yellow lightsaber sometimes used the dark side of the force kind of like Luke did in Return of the Jedi.
I think it would be cool to see this color be brought to the films and maybe even J.J. Will sample from the EU and give Rey a yellow lightsaber which is usually the symbol of balance. Maybe I’m getting my hopes us but I really do hope they use this color in the films. Honestly it makes the most sense for Rey to have the yellow lightsaber in the next film or even in Rian Johnson’s trilogy. Whatever the case I have a feeling we’ll be seeing yellow very soon.