If you are upgrading from earlier versions of Gnome and try to upgrade your 1.x version of x11-themes/gnome-icon-theme to 2.8.0 it will fail at testing as x11-themes/hicolor-icon-theme is missing. Reproducible: Always Steps to Reproduce: 1. emerge x11-themes/gnome-icon-theme Actual Results: At test stage fails as x11-themes/hicolor-icon-theme is missing Expected Results: A dependency check should have been done and forced an emerge of x11-themes/hicolor-icon-theme. x11-themes/hicolor-icon-theme hasn't been a priority for me before, as both KDE and Gnome2 icons themes are stored in the same place and they tend never be compatible with eachother, so ther would be all to many icon themes to select from which don't work under KDE (would be smart to store the icons themes in different places).
if you had checked the ebuilds, you would've seen it's there and has been for a long time.
Then there is something wrong in the portage system, as the x11-themes/hicolor-icon-theme wasn't automatically emerged, it had to be emerged manually... sorry for missign the check of the dependencies in the ebuild.