I figured out the problem - wxia3 defines ".selected" and gives it several properties, including the color red. This is then inherited by the selected class used in tabcontent2.css.
I'm assuming you can't easily modify wxia3 without screwing up a whole lot of existing stuff on your webpage, so I would rename ".shadetabs li.selected" to ".shadetabs li.selectedtab" or something like that (You'll also need to change tabcontent.js so that all references to the "selected" calss become "selectedtab" but you probably know that already).