No actual manual at least not a detailed one. I guess there have been so many changes Rick just has not had time to put one together. Now we have version 8 on the horizon so it will be different again.
As far as appearance goes it is all css based in the control panel under styles.
What you may want to do in install some extra styles at ubbskins.com.
Then you could play with them without hosing up your existing styles
