The Tango Desktop Project provides special patches for KDE 3.5 to improve the integration of the icons (x11-themes/tango-icon-theme) into the desktop. The patches are rather minor and have to be applied to kdebase and kdelibs (or the appropriate split ebuilds). I'd suggest to add the patches to the KDE ebuilds as long as the 3.5 series is marked unstable. An upstream bug report has been filed [1], but is postponed due to string freeze. [1] https://bugs.kde.org/show_bug.cgi?id=120562
This will be left for upstream to decide.
*** Bug 136442 has been marked as a duplicate of this bug. ***