If you are using Menucool's Responsive Tabs, it will be much easier as it has equipped with a callback handler:
function onTabSelected(tab, panelId) {
tab.style.backgroundColor = "yellow";
}
Tabbed Content doesn't seem to have that handler. Maybe you can try adding the event handler to the tab's HTML markup:
<li onclick="this.style.backgroundColor='yellow'">...</li>
I didn't test it. You can try it out and post back if it works.