Sith Eyes

[unspeakablehorror]

The yellow Sith eye effect seems to be very specific to the Sith.  Like it's not something every darksider in the canon has, and it doesn't seem to necessarily correlate with the intensity of evil a character possesses, either.  Even if we look at characters pre-sequels, Ventress didn't have Sith eyes, but I believe this was simply because she was never fully trained as a Sith and so never participated in whatever portion of Sith custom causes that specific feature.  Whereas all the Darth Siths did develop that trait, (ie Sidious, Maul, Dooku, and Vader).  But neither Snoke nor Kylo Ren developed the Sith eye trait, and I believe that's not due to some lower intensity of their evil, but rather because neither are Sith but instead follow some different and currently unclearly described Force custom.

At some point I want to refine my own headcanons for the specific reasons behind this, as it is relevant to my fic.