For many years the hue of the lightsaber has been known as blue, green and red. As more and more stories emerge, the lightsaber has grown past just three basic colors. In non canon we see as many as 8 to 10 colors. In canon we see 6. The hue is affected by the Kyber Crystal, also known as a lightsaber crystal.
In the old canon (Expanded universe) it was described that the Sith had red lightsabers. The color red was because of a synthetic Kyber Crystal. Synthetically made Kyber Crystals only gave the red hue and were said to not burn as hot as organic Kyber Crystals. The Sith found it very hard to obtain organic Kyber Crystals because the Jedi held them in a sacred place.
In the Cartoon Network series ‘Star Wars: Clone Wars’ we witness a tradition known to padawans as obtaining your lightsaber crystal. This happens in a cavern that is full of Kyber Crystals and traps. This was a very neat episode where we learn a little more on what it takes to make a lightsaber. Just like you see in ‘Harry Potter’, the wand chooses the wizard, we see in Star Wars. The Kyber Crystal chooses the Jedi.
This made it very hard for Sith to obtain crystals. Kyber Crystals don’t call to Sith. So the Sith hunt down other crystals. In the new Canon book ‘Ahsoka’ it is described that the Kyber crystals “bleed” when taken by the Sith. Now since the Kyber Crystal do not call out to the Sith, they have to bend the will of the Kyber Crystal itself. When this happens the crystal releases a red hue. This hue will stay red for as long as the Sith wield it. The crystal can be saved by a Jedi, but when this happens the Kyber Crystal looses all color and becomes white.
Everything we thought we knew about lightsabers has changed from this new book. Many questions come to mind with this new information. Why does Ahsoka have white lightsabers? Is Kylo Rens crystal cracked because he is trying to bend its will? How long can a Kyber Crystal bleed for? Hopefully we will see more information on lightsabers in the new movies and TV series. Lightsabers are a unique weapon for a more civilized age.
Diary of a Sith Chick 
Some of these little details they’ve been adding I just don’t understand…what’s even the point of mentioning that crystals “bleed?” Granted, I haven’t even arrived at that point in the book yet, but I still doubt it’s necessity…
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I think it’s an explanation to the red color of the lightsaber. As the canon timeline goes they have thrown out the making of synthetic crystals. Now the sith obtain their crystals from defeated foes or they take them from old Jedi Temples. I won’t spoil the book for you but I think Ahsoka makes a good point when she talks about it.
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