I've farmed these off and on in prommies for over a year now, killing well over 2k mobs. Somber memories only drop from the mobs with ice affinity, it's strange that a water based memory drops from an ice based mob, but it has been verified by testing the mobs resistance to ice. Each color mob can drop the memory associated with it's particular color, and may also drop a second memory that is either malevolent or radiant depending on the light/dark affinity of the mob. Dark color mobs will drop either one or two malevolent memories and light color mobs will drop either one or two radiant memories.
I'm not sure if this was changed at some point, but somber memories do NOT drop from all dark-based empty. Somber is unique to ice only, it's malevolant memories that drop from all dark-based empty.
Yes, Valent and Ettalo are correct. Memories are unique to one specific elemental type of empty. You will never receive a somber memory from a water based empty, nor a dark aligned empty. It is an impossibility. FFXI Wikia has been updated with these corrections and a new page for "Memory" has been added.
@Kittiara: The Demand on these dropped hardcore recently, when demand goes down, sometimes you're forced to drop the price, also, hike up the price too high, and no one will buy
it's crazy how this Ughness guy keeps underselling himself. when i was farming these a month or 2 ago they were 200k a stack. this guy makes no sense, he is the only one selling them on Valefor pretty much and lowers the price on himself. hmmmmm
@ Karubuncle They can also drop from Earth based. All memories come from their particular light or darkness skillchains. So all Light based memories can come from all light based mobs and all dark based can come from all dark based mobs.