WorldClient has themes, and then different styles for each theme. If you'd like to force users to have a defaulted style and theme, add the following to the \MDaemon\WorldClient\Domains.ini file:
[Default:UserDefaults]
Theme=Standard (or other theme name)
Style=Contour (or other style name)
This should default all users who have not specified a theme to the Standard theme and the Contour style.