I noticed on Kubuntu 12.04 Beta 1 that GTK apps have tooltips with dark background and black font. This is related to the oxygen-gtk theme used for gtk applications. When I change in systemsettings -> application appearance -> gtk+ appearance and select Raleigh as theme instead of oxygen-gtk then I get dark background with white font. I noticed that black font on dark background in Thunderbird, LibreOffice-gtk, Chromium and Gimp. As soon as I change to the Raleigh theme, all tooltips are readable.
Can't reproduce. Likely an issue with kde's attempt to set gtk's colors, overlapping with oxygen's attempt. Make sure files such as $HOME/.gtkrc* and $HOME/.kde*/share/config/gtkrc* don't contain any color settings. Also, in systemsettings->applications appearance->colors->options, make sure "Apply colors to non-kde4 applications" is unchecked. Please close the bug if any of the above fixes it.
Ah, "Apply colors to non-kde4 applications was checked. After unchecking it all seems to work fine.
ok. So closing :) thanks for reporting !