unfortunatelly there is still no plug'n'skin and it will be migrated after final.
1) you could extrack skin files from richfaces-impl rename and customize what you need.
2) then you could look into the component ecss files from richfaces-components-ui files to provide your own rf-* classes with custmized skinning.
Is it possible to include images using skinning ?
as usually in bg-image properties in your ecss files..