Getting the staff of light.
The Waylumi Priestess within the Waylumi Cathedral, assigns you to help in the efforts of rebuilding cathedral, even though the lazy bitch hasn’t done a thing about it in 15 years or more. 
She needs three  crystals to help make your staff of light. 
What kind of crystals you use do not matter, but the thing to keep in mind is that the special does not change no matter what color crystal you use.
So use the blue crystals as its easier to acquire and more cost effective.