I've made a replacement package for rootskel-gtk, using the previous version rootskel-gtk_1.27 as the source, and placed it in each of the following folders, one at a time and cleaned the cache and done a build. rootskel-gtk_1.27_amd64.udeb still appears in the cache/packages.binary_debian-installer.udeb folder, and the new theme is not used.
config/packages.binary/ config/includes.debian-installer/ the new version of rootskel-gtk is a later version than the one from the wheezy debian repos and contains a new logo in /src/usr/share/graphics and updated theme in /src/usr/share/themes/Clearlooks/gtk-2.0 live-build version 3.0.5-1
