So, that's the real reason Anakin's saber didn't change color -- because the process of lightsabers changing colors (after bleeding) didn't exist as a concept when Revenge of the Sith came out. At the end of the film, Darth Vader loses his lightsaber during his duel with Obi-Wan.
Anakin's Third Lightsaber (Red)
Anakin traveled to the river moon Al'doleem to do just that, slaying Jedi Master Kirak Infil'a and confiscating his lightsaber. This was a curved-hilt saber with a green blade. From there, Anakin went to Mustafar to bleed the kyber crystal and turn it Sith red.
Blue. Because it looked freakin' cool in the 1970s. And Luke's father used a BLUE saber according to Obi Wan. So Anakin has to use a blue saber or he wouldn't be able to be Luke's dad.
After pledging himself to the Sith Lord Darth Sidious, Anakin Skywalker took the name Darth Vader but continued to use the blue-bladed lightsaber he'd fought with during the Clone Wars. He lost this weapon on Mustafar and constructed a replacement with the crimson blade favored by the Sith.
Some fans have wondered why Anakin's lightsaber is green in Episode 2 but blue in Episode 3. George Lucas has explained that the color change was a deliberate decision, made to reflect Anakin's emotional state at the time.
It's because of his mastery of sorsue (sorry for my bad spelling.) Well if you want the ACTUAL reason it because in the original 3 films the Green Light Sabre didn't exist until after Obi Wans death.
Affiliation. This blue-bladed lightsaber belonged to the Sith Master Darth Sidious after his resurrection on Byss. Darth Sidious using the lightsaber to battle Luke Skywalker. In his lab on the Imperial throne-world, Darth Sidious kept a number of stolen Jedi lightsabers if he needed them.
Originally the weapon had a blue blade, but after his destruction of the Jedi Temple and fall to the dark side in 28 ABY, Ren modified it into one with a red blade.
Leia Organa's lightsaber was a blue-bladed lightsaber powered by a kyber crystal in the core of the hilt. It was silver and copper in color and featured mother-of-pearl inlays. Organa's weapon was considered a work of art, having an elegant symmetry with silver and gold hues that evoke to her upbringing on Alderaan.
Luke Skywalker's lightsaber was changed from blue to green when they were filming because it was difficult to see. This became apparent during act one of Return of the Jedi when the battle on Jabba the Hutt's sail barge was shot during the day. The blue lightsaber blended in with the clear blue sky.
Terrio describes Rey's journey to Tatooine as a pilgrimage honoring the Skywalker family heritage, saying: “Rey brings the sabers there to honor the Skywalker twins by laying them to rest—together, finally—where it all began.
A crystal embodies the Jedi as the heart of the lightsaber, and pure kyber has no color until it's bonded to the Force user. This process likely resulted in Rey Skywalker's lightsaber being yellow.
In Star Wars: Revenge of the Sith (2005) when Obi-Wan dismembered Anakin we see his eyes permanently turn yellow as a sign of him fully being corrupted by the Dark Side. Prior to this his eyes changed eye colour off-screen from one scene to another depending on the situation.
Relatively recently, Star Wars canon established that the reason a red lightsaber is red is because the crystal bleeds after the user does something really, really bad. Meaning, your lightsaber can change colors, and Rey's has changed colors because she's done something bad enough to cause the crystal to bleed.
Obi-Wan Kenobi has been one of the few main characters in Star Wars that hasn't been tempted by the dark side, but one episode of Star Wars: The Clone Wars shows the Jedi Master wielding a red lightsaber traditionally synonymous with the Sith.
Some Jedi are explicitly shown using red lightsabers in Legends, however. This includes Adi Gallia, Even Piell, Depa Billaba, A'Sharad Hett, and even Luke Skywalker.
The lightsaber's amethyst color was chosen by the actor portraying Windu, Samuel L. Jackson, who wanted a purple lightsaber because he was "the second baddest Jedi in the universe" and so he could find himself among the many Jedi featured in the Battle of Geonosis scene.
After the duel, in which Padmé was victorious, the weapon was wielded by Skywalker for the rest of the Clone Wars. Padmé used this lightsaber for many battles to come.
After losing his father's lightsaber on Cloud City, Luke Skywalker constructed a replacement with a green plasma blade, its hilt similar to that of Obi-Wan Kenobi's weapon.
Even though Kylo Ren uses a red lightsaber, harnesses the dark side of the Force, and wears a cape, he is not a Sith. Because of that, he can never hold the title of Darth.
Yoda's lightsaber was smaller than a standard Jedi lightsaber, befitting his shorter stature. But its green plasma blade was every bit as deadly in combat.
Rey's lightsaber was a yellow-bladed lightsaber that was constructed by the Jedi Rey Skywalker following the First Order-Resistance War.
Black lightsabers are extremely rare in the Star Wars universe, and only a few have been seen on screen. These lightsabers are typically associated with the Dark Side of the Force and wielded by Sith or Dark Jedi. The most well-known black lightsaber is the Darksaber, which was created by the first Mandalorian Jedi.
Bleeding Crystals
Because the crystals are borderline sentient, they refuse to work with those who follow the dark side of the Force, so the Sith must resort to a process called bleeding.