In order to emulate more closely the look and feel of the Outlook 2010 ribbon bar, it would be nice to be able to separately specify an inactive border color for TabPane, so the inactive tabs can be made to look more in the background. This would also allow a mouse hover to be written that will highlight the inactive tab that is under the mouse, to emulate the Microsoft look-and-feel.
By setting the default to the same theme color as the (active) border color, the behavior should be the same as before unless an application explicitly sets the border color. It could also be setup so that setting "borderColor" affects both, so that "inactiveBorderColor" would have to be explicitly called afterward in order to change it. Not sure how important this backward compatibility would be.