Although Order 66 played a large role in Anakin Skywalker's corruption in Star Wars, it wasn't his point of no return. Despite being sent by Palpatine to kill all the Jedi on Coruscant, Anakin's fall to the dark side wasn't complete until his mission on Mustafar. This is ed by some key evidence regarding Anakin's eyes and the nature of the dark side itself.
As seen in Revenge of the Sith, Palpatine's plans to erect his new Empire out of the ashes of the fallen Republic came to fruition, and the first steps were seducing Anakin to the dark side and the eradication of the Jedi Order. While clone troopers were used to execute Jedi all over the galaxy via Order 66, the newly christened Darth Vader personally led the 501st Legion to kill those still inside the Jedi Temple on Coruscant (including the younglings). However, a key detail proves that the massacre wasn't Anakin's point of no return in the Star Wars continuity.
Anakin Saw Order 66 As A Grim Necessity - Meaning He Didn't Surrender To The Dark Side
Palpatine intended Anakin's massacre at the Jedi Temple to be a version of a Sith ritual. Traditionally, a Sith apprentice would prove themselves by killing someone of value to them. However, Anakin's eyes only turn the yellow of the Sith after the initial events of Mustafar. This is likely because the attack on the Jedi Temple was nothing more than a grim necessity from Anakin's perspective, something he had no choice but to do in order to save his wife and bring peace and order to the galaxy according to his new master.
The lack of Anakin's yellow Sith eyes during the events of Order 66 are further ed beyond Revenge of the Sith. As seen in Obi-Wan Kenobi, flashbacks to the slaughter at the Jedi Temple see Anakin killing Jedi and younglings without his eyes having turned. As a result, there's a very important reason why they did turn yellow once Palpatine sent his new Sith apprentice to Mustafar.
Anakin Only Surrendered To His ions On Mustafar
In contrast to the massacre he led on Coruscant he felt he had no choice but to carry out, Anakin's mission to Mustafar saw him fully giving into his ions and hate as a Sith Lord would. Killing the Separatist leaders motivated Anakin to indulge in his ions, getting revenge on those he'd come to hate during the events of the Clone Wars. As such, this is why his eyes turn yellow after this second massacre (and not before). It's only when Anakin has given in to his ions that he has truly bound himself to the dark side in Star Wars, truly becoming Darth Vader on Mustafar.
