I can't find a way to change the background color of the active tab widget. The default is barely distinguishable from the rest of the tabs. Is there any way to do this or is the color hard coded? Thanks!

Short answer: No

Long answer: Yes, it should be possible.

There is a hidden option for the stylesheet of tabbar since KDE SC 4.9. So if you are familiar with QStyleSheet[1] syntax, you should be able to customize the appearance of the tabbar. Here is one example of using bold font for the active tab.

# in ~/.kde4/share/config/konsolerc
[TabBar]
TabBarStyleSheet=QTabBar::tab { min-width: 2em ; max-width: 25em } QTabBar::tab:selected {font: bold}

Note, that option is hidden, so there is no guarantee that it will work well. Use it with care.

[1] http://doc.qt.digia.com/qt/stylesheet-syntax.html