One can set the tabbar background pixmap like this:
mrxvt*tabbarPixmap:
/home/luis/.mrxvt/tabbarbg.png
It should be possible to do the same for the tabs:
mrxvt*tabBackgroundPixmap:
/home/luis/.mrxvt/tab.png
mrxvt*itabBackgroundPixmap:
/home/luis/.mrxvt/itab.png
This way the active tab may get more visibility with a
different pixmap.
See the attached screenshot that shows what I mean.
luismsgomes@gmail.com
Screenshot