BUG: Update default module icon color

Commit r22288 associated a default icon with all modules. Then, as
suggested by Wendy Plesniak this commit changes the icon color to
be "SlicerBlue".

See #3293

Co-authored-by: Wendy Plesniak <wjp@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22291 3bd1e089-480b-0410-8dfb-8563597acbee