This probably does not exist in Zenphoto but is there anyway to add a unique class to the body of each page/album/sub-album in ZP (something similar exists in Wordpress). This would allow one to quite easily change the style of any page separately from the others...

You should see if the mutiple_layouts plugin provides what you want.

Of course, your theme can always make whatever check it wants and load an appropriate CSS file. For instance several of the standard themes have the CSS scheme selectable by an option.

As to the "class", that could be a unique tag or some data placed in the "custom data" field.

Thanks
That's a few different possibilities to investigate.