Theming docs

[Sam]

Hi! I'm pretty new to this, but are there any docs for creating themes? 
Also can I place them in /usr/local or /etc instead of /usr?

Is it possible to just add a custom distro watermark, like the one 
fedora has, to a pre-existing theme without putting it in /usr instead 
of the above mentioned locations? (note: would be nice if there was a 
way to not copy the whole theme over)

Also is this the right place for these types of questions?