As Star Wars fans may recall, after Anakin succumbed to the dark side in the second half of Revenge of the Sith, his eyes turned yellow. But there’s more to this transition than most people think.
While the first two movies in George Lucas’ Prequel Trilogy depicted the heroic deeds of Anakin Skywalker and his rise from a Force-sensitive toddler to one of the greatest heroes of the Republic, the third film revolved around him completing his tragic fate and turning to the dark side. When he did, Darth Sidious’ new apprentice went on a killing spree, starting at the Jedi Temple. Having slaughtered the younglings, Vader then made his way to Mustafar to kill the Separatist leaders. In one of the movie’s most iconic scenes, the Chosen One mercilessly dispatches the people who fought him during the Clone Wars. 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. When Anakin and a platoon of the 501st make their way to the Jedi Temple, his eyes are their usual color, because he has yet to commit his most detestable act. When we see him on Mustafar, this is a special situation for the former Jedi Knight, considering his deep resentment towards the Separatist leaders, especially the infamous Nute Gunray and Wat Tambor. Surprisingly, when Anakin talks to Padme later on, his eyes have turned back to their bluish hue.
In that sequence, since Anakin was in the presence of someone he loved, he wasn’t channeling the dark side as strongly as before. But even as Vader in his suit of armor, we briefly saw Anakin’s yellow eyes when Ahsoka cut through his helmet during their encounter in Rebels.
It wasn’t until finding redemption after saving his son at the end of the third Star Wars movie and the last installment in the Original Trilogy that Vader finally let go of the dark side and became one with the Force.