Why are the light sabres, as used by the Sith in Star Wars films, red in colour? The Star Wars wiki tells us,
While the Jedi used natural crystals, the Sith mostly used red-hued synthetic crystals.
In today's Darth Vader #1 comic book by Charles Soule, Giuseppe Camuncoli, Cam Smith and David Curiel, and published by Marvel Comics, that is done away with. And remember, these comics are intended to be Star Wars canon.
Set immediately after the end of Revenge Of The Sith, the Emperor and the newly armoured Darth Vader talk/
Is that just colourful language? No, not really. Checking in with Star Wars Wiki…
Kyber crystals, also called the living crystal or simply the kyber, and known as kaiburr crystals in ancient times, were rare, Force-attuned crystals that grew in nature and were found on scattered planets across the galaxy. They were used by the Jedi and the Sith in the construction of their lightsabers.
Instead, Darth Cader not only states that Sith light sabres are made from kyber crystals stolen from Jedi knights… there is torture involved.
No wonder they scream when you wave them about.
So there you go. A new canon explanation for why the light sabres of the Sith are red. Because the kyber crystals that form the weapons have been tortured to agony by the Sith mind, using the Force.
Sleep well now.
Wommmmm…. wommmmmmm…. wommmmmm….