A Google search for "dark of peace" turned up the following:
http://profs.logti.etsmtl.ca/mmcguffin/McGuffin/
That is all rather interesting stuff about very old Scottish clan names which seem indeed to revolve around concepts like "dark" and "peace" somehow, but exist in many changed, shortened and anglicised forms and seem to come with a "Mac" in front anyway.
And now a given name Fia is connected to MacFie or whatever variant of that? Well, maybe - a very big maybe, if you ask me!
Rene www.AboutNames.ch