Most of the nerds on this site probably know this, but the color white in MTG is typically associated with goody two shoes characters like priests. Whereas black is traditionally the color of evil creatures like undead. So the white-black hybrid designation refers to the conflicted nature of Sachi's grandfather as a former religious leader and current undead abomination.
If this were MTG his colour would be white-black
My friend who plays Magic a little tells me that this is basically chaotic goodSachi's grandpa will be pleased!Side AThe theme for the next concert is zombiesCool and dark, huhSure, why noooootttt?UndeadBut my gramps is a priest, you know~