Demon's Souls will take pity on the masses this holiday as the game shifts to the "pure white tendency" this holiday. What this means is that "new areas and special NPCs" will exist in Boletaria during that time -- as a bonus, enemies cause less damage and players inflict more. Pure white is not easy to achieve, so this is a great opportunity for players. Atlus does note that adventurers may need to "log in and out a few times before [the] tendency shifts to match the server."
Demon's Souls had a similar event during Halloween, but that was "pure black." There is no shame in using the game's official wiki and, for soul's sake, we recommend using it.
Update: We followed up with Atlus and received a more specific time for the event: "Noon PST to noon PST, 12/21-28." Happy hunting!