@Karlyle
Sorry, again not sure if I get you right...You are bothered that sometimes you type something what then doesn't go to the currently selected tab? There used to be an option (<o>-key) "Interface/Chat/Default last chat" (I think). If I remember right that one will put a /tell" automatically in front of every chatline you type after you used tell. So turn off that crap and everything you type should go in the current selected channel...no matter in what channel you typed before or if you started typing in the tell channel and just switched to the guild channel before pressing <enter>. It will go in the channel that is active at the moment you press <enter>.
@Bonifarzia
It works fine with PS revision 7118 which is about a month old. (Sorry, can't be bothered to try with a current version and solve all the conflicts in my sourcecode when syncing again). My window Title says 0.5.7...no idea what the current version is.
And just because I was confused by it at first:
In "data/art/skins/elves.zip/imagelist" the first rectangle (the red one in my sketch) is called "Standard Tab". Still that is the one that is responsible for the highlight. Too lazy to look up why this is the case but after the trial and error method and giving all three different colors that was the right one for me. The "Standard Tab Highlight" one changes the background of all not-selected buttons.
Oh..and btw, sorry for the typo in your name. Forgot to proofread the post before clicking submit. ;)