Corrupted GTK theme for Ubuntu Tweak

I am facing a problem related to corrupted gtk theme with Ubuntu Tweak. My default theme is Ambiance under Unity. It works fine for most applications like Chrome, Firefox, Nautilus, etc. However, for applications such as Gnome tweak tool, Ubuntu Tweak, etc. the gtk theme is completely black and dark. That is the background window color, making viewing the window text very difficult.

This is happening with Gnome shell also. I have tried resetting gnome and Unity settings, reinstalling light themes, but it didn't work.

This is a link containng a screenshot that I posted in askubuntu.com: http://askubuntu.com/questions/101502/corrupted-theme-for-certain-applications#comment117271_101502