Anakin temporarily got yellow eyes as he was killing the separatists on Mustafar, a dark and treacherous deed. His eyes again turned yellow after Obi-Wan managed to maim him, and we must assume that his consciousness was reduced to a scream of pain and impotent hatred. That's a Dark Side thing.
It didn't really become a pattern until Anakin completed his turn to the dark side. Anakin's eyes go back and forth over the course of Revenge of the Sith. When he's slaughtering separatists on Mustafar, they're Sith yellow, but when he's dueling with Obi-Wan, they've gone back to normal.
Though Anakin was Palpatine's apprentice at that time, he hadn't full turned himself over to the dark side yet and was just starting to follow the path. Ultimately, Anakin's yellow eyes serve as a visual representation of his descent to evil, a cue for audiences to pick up on while watching the film.
It's here that a close up of Hayden Christensen's face shows that Anakin's eyes have turned yellow. In Star Wars lore, it's agreed upon that when someone's eyes turn yellow, they have fully embraced the dark side of the Force.
Originally a slave on Tatooine, Anakin Skywalker is a Jedi prophesied to bring balance to the Force. He is lured to the dark side of the Force by Chancellor Palpatine (Darth Sidious) and becomes a Sith Lord, assuming the name of Darth Vader.
Really, the yellow eyes of the Sith show the physical toll the dark side issues on its 'host' if you can call it so. It represents the dark power within them, the unchecked and even unbalanced rage swirling through their body. Kylo Ren was never fully immersed in the dark side, as was evident throughout the movie.
Of course, Sidious didn't tell Dooku the full plan, so that didn't work out too well for him. Regardless, Dooku's eyes weren't yellow because he wasn't motivated by anger. He was merely a practical dark side user, so he does not have the usual Sith eye color.
Palpatine was in all actuality a very deformed Sith Lord from decades of using the Dark Side. To hide this, he used force mask, which also hid his yellow eyes. Of course when Mace Windu destroyed the mask in their duel, Darth Sidious' true form was exposed.
Some have even speculated Sith can grow addicted to Force lightning. This naturally explains why Jedi do not generate Force lightning. Jedi seek to master their emotions rather than be mastered by them; Force lightning is therefore forbidden, as it is best understood as a spontaneous outpouring of hatred and rage.
“The tear [on Anakin's face] says that he knows what he's done, but he has now committed himself to a path that he may not agree with… but he is going to go on anyway. It's the one moment that says he's self-aware that he's rationalizing all his behavior.
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.
His unbalanced rage allows the calmer Ventress to play with the Jedi Knight, ultimately landing a face blow with her saber that produces Anakin's scar. The pain of the scar, while not posing much of a threat to Anakin, does reveal how far to the Dark Side he is slipping.
Obi-Wan knew Anakin through and through and understood his overconfidence and arrogance. He knew Anakin would fight with rage and aggression, while he remained cool and calculated. Pairing his understanding of Anakin with his knowledge of Soresu ultimately gave him the upper hand in the battle.
In the original 1982 teaser trailer for Return of the Jedi, the color of the lightsaber was blue. The decision to change the color of the lightsaber from blue to green was made to make Luke's blade contrast with the blue sky of Tatooine and make it more visible during the skirmish at Carkoon.
palpatine was a master of deception. and for years. he employed the use of a sith cloaking technique. known as a force mask.
You will notice that some sith such as Count Dooku and Yoda does not have the yellow eyes. They fail to get them as they have not fully embraced the dark side which means they enjoy self-control.
Sidious may have given Dooku the title of Darth Tyranus, but because the Jedi Order knew him as Count Dooku, greatly preferring to not indulge his role as a Sith, they continued to call him by that name.
Trioculus is killed by a droid replica of Princess Leia. Triclops is Palpatine's illegitimate son, named because of his three eyes. He is sent into solitary exile because the Emperor fears Triclops' potential mastery of the dark side of the Force.
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. Instead, he was just a chaotic mess of the dark side (until he eventually found his way back to the light).
In The Phantom Menace Obi-Wan says, "The reading's off the chart. Over 20,000. Even Master Yoda doesn't have a midi-chlorian count that high." Anakin was stronger however, he didn't really master his powers until he became Darth Vader. ^ that just means he had more potential than Yoda.
Count Dooku became a Sith because the Jedi served a corrupt Republic, but he had another more personal reason to betray the order. The following contains spoilers from Yoda #4, on sale now from Marvel Comics. Darth Sidious was Star Wars' master schemer.
In Star Wars: The Last Jedi, we learn that Rey and Kylo Ren's connection to each other via the Force, a strange power that allows them to communicate and even touch across vast distances of space, was concocted by Supreme Leader Snoke.
Kylo Ren's helmet was a battered, face-concealing black combat helmet with a silver inlay that radiated from the eyes as a symbol of power. Modeled on the battle gear worn by the Knights of Ren, the helmet served to hide Ren's former identity as Ben Solo—the nephew and fallen apprentice of Jedi Master Luke Skywalker.
A dark side warrior with a mysterious past, Kylo Ren was neither Jedi nor Sith, but a product of both sides' teachings. Once an apprentice of Luke Skywalker's, he killed his fellow students and drove Skywalker into exile, becoming a First Order warlord and servant of Supreme Leader Snoke.