Comment 7 for bug 1329811

temporary solution:

  apt-get source compiz-plugins
  sudo apt-get build-dep compiz-plugins
  # edit compiz-0.9.11.3+14.04.20141104/plugins/staticswitcher/src/staticswitcher.cpp
  # line 257
  # attr.background_pixel = 0x13579246;
  cd compiz-0.9.11.3+14.04.20141104
  dpkg-buildpackage -b
  cd ..
  sudo dpkg -i compiz-plugins_*.deb
  # restart unity to see changes
  unity

Play with background_pixel (4bytes), last is transparency. To avoid compiling you can search for value 0x13579246 in hex editor (file /usr/lib/compiz/libstaticswitcher.so)