When the collection is complete, you can turn it in to any Collector NPC for your reward and a very nice chunk of experience.
The purple shinies inside An Icy Keep are only visible once you have started the third quest in the Frostfell 2008 Ice Dragon series, Covering Your Snow Tracks!. You will still be able to see them after completing the quest.
In the Frostfell Wonderland Village there is no prerequisite to see them. They are plentiful, mainly on the ice, and respawn quickly.
Occurs annually during the winter holiday season.
Introduced for Frostfell 2008.