Found what could be a solution to your problem here
Basically it says you can retrieve children from your TabBar as Button, since Tab extends it. Using Button instead may help although I'm not sure why applying these styles would not work on the Tab itself. On one of my project, I've been using .setStyle on "chromeColor" to apply the connected user's color on some of my app's button.
You could also be using CSS and states to accomplish this, but maybe it won't be necessary for basic styling.