Be mindful Sith weren't the only ones known to carry a red-bladed lightsaber. Some Jedi did carry a red-bladed lightsaber like Adi Gallia. She wasn’t one to stick to tradition just because it was expected. She made choices based on what would get the job done. That’s why, for a time, she carried a red-bladed lightsaber. She's just 1of 4 Jedi who were known to carry a red-bladed lightsaber.
There’s a color that was overlooked: at one point during the Clone Wars series, Ahsoka’s secondary shoto blade is a yellowish-green that is distinct from her main green lightsaber. I imagine that such a middle-ground color might represent a blending of both green and yellow, a Jedi that is still guided by wisdom and philosophy, but is more active in their sense of duty than traditional philosophers that might be more passive and introspective. Given that Anakin was Ahsoka’s master and was well-known for bold, decisive action, bordering on recklessness, in service to the Republic, some of that decisiveness could have rubbed off on Ahsoka and influenced her when it came time for her to build her second lightsaber.
The color spectrum of lightsabers reminds me of the color spectrum of the Lantern rings. Seeing different colors of lightsabers in the cannon is good to see, hope to see cyan, indigo, & magenta in live action or animated would be cool!
For some reason, growing up, I always assumed green meant the wielder was now a Jedi Master. Turns out anyone can have one and it's not a signifier of rank
When it comes to yellow, there's also the fact that no one has obtained a yellow crystal for a long time, the temple guards inherit their yellow lightsabers. So rey having a yellow blade at the end is a symbol of the jedi moving on from the previous era, one that no longer created yellow lightsabers due to the dogma that led to their downfall.
I know there's no lore behind this one, but since getting the color in KOTOR, I choose a Viridian lightsaber: a silver-green color. I like to think that it's a color saved for the rare Jedi who have deep connection with the Force, yet is grounded and jaded enough to practice their own justice when necessary.
Not sure someone already pointed out but in KOTOR there's an orange colored lightsaber as an option if you head towards the space station near Yavin 4. So Cal Kestis is not the first Jedi to wield it technically. It was Jedi Revan from KOTOR