Easy. The site's default theme is an eleven variation version of the original Outline theme. I coded the changer buttons at the top as part of it. That way it can be used on forums that don't run a portal with a theme changer (also multi themes end up with a much smaller files size than eleven separate themes and they are easier to edit for mods).
The others are separate themes. Mystic is obviously another multi, as is the TP_Default, while the rest of them are singles.
I like changing my themes now and then, keeps it more interesting.