Ben had a Yellow Kyber Crystal
In TFA script it is described as
We know that Kyber Crystals Bleed if they are bent to the will of a Darkside user. Kylo is not all dark nor all light. I am willing to bet money Ben’s crystal was once all yellow.
Adam driver even said the crystal is unstable just like Kylo. It’s a metaphor.
What if his crystal split in his original lightsaber prompting him to build a new one with the vents to help stabilize his kyber. Just as he would need to build a new identity for himself as Kylo Ren, crude and unfinished.
What is more important about the color yellow is that it was primarily used for the Jedi Temple Guards. Couple that with Kylo’s knight like design you get a man on a crusade. A Knight who right now has been corrupted in his duty.
Ashoka purified her blades to white after taking them from a dark side user. Could Ben’s return to yellow in the end if he is redeemed and stabilize? This would be a beautiful choice of visual storytelling if they go this route. It matches his cross guard hilt perfectly. I hope so I want his to be yellow.
PS Yes I realize that the script could have just been describing the color to show its fiery nature but if they weren’t that’s a huge clue. Fun speculation though.