Ok. You defined the searchable topics in the hidden value (Which can be edited by everyone via inspect elements).
People can change which forums they want to see via the live search. Even hidden forums (Think about a forum only for administrators, moderators etc.)
So they can get the topics in the hidden forums. Not a big problem, but what if you include secret information in the topic title?
Hidden input > GET Parameter > Your PHP file > Query.. without any checks.
I like your idea, however your implantation looks a little bit strange to me. Why not prototype and ajax? That would make it even easier for you. So imho the implantation is bad (sorry :P) But overall a good hook and addition for my board. Thanks!
But it is an inline css (<p style="color blablabla"></p>) So i am almost sure its not a problem from my skin. Also installed the skin on an other board but i cannot reproduce black colors :S. Someone else?