Good point about Superman and Spider-Man. In fact, seems like a lot of main characters are red. I do get where you're coming from, though.
From a story-based standpoint, it does make sense that Cal can't use Trilla's crystal since his psychometry would probably incapacitate him like it did on Bogano, and even if it didn't, he might have some moral issues with using it intentionally. I don't remember specifically, but isn't there some lore in the new canon about the kyber crystals being alive and turning red only when tortured? Cere probably wouldn't have used the saber if she'd had another choice, but then again, she was already toeing the line a little.
