User blog comment:Disfigure/This was only shown in the Anime about Guren Ichinose/@comment-25942629-20160208212128

The candy cane swords? It's hard to say since we know diddly about the vampire weapons. Guren's sword is red on the manga color page for chapter 13, the very same image you're using for your avatar. It's also red in the bonus chapter with Yu in the overalls that takes place after Yu escapes from Sanguinem and has been living in the human city for awhile. It's also red on Vampire Reign volume 8 and the color spread for chapter 32. In Guren's case, I think it's just the sword and has nothing to do with drinking blood. It could also be Guren's personal aura or something since the first Catastrophe light novel shows him using a red sword, and that sword is different than the one he's using now.

I don't know much about the vampire weapons, but Guren's sword turns red just fine without drinking any blood.