The WebUpd8 Themes PPA has updated Zukitwo GTK2/3 theme that makes the theme use a regular panel background by default (dark) in ubuntu 11.04 and 11.10.

Ubunu 10.04 and 10.10 user have to run following commands to customize panel background,

For Zukitwo:
sudo sed -i 's/#bg_pixmap\[NORMAL\]/bg_pixmap\[NORMAL\]/' /usr/share/themes/Zukitwo/gtk-2.0/widgets/panel.rc

For Zukitwo Dark
sudo sed -i 's/#bg_pixmap\[NORMAL\]/bg_pixmap\[NORMAL\]/' /usr/share/themes/Zukitwo-Dark/gtk-2.0/widgets/panel.rc

For Zukitwo Resonance:
sudo sed -i 's/#bg_pixmap\[NORMAL\]/bg_pixmap\[NORMAL\]/' /usr/share/themes/Zukitwo-Resonance/gtk-2.0/widgets/panel.rc

Now, install Zukitwo theme in ubuntu using following commands:

sudo add-apt-repository ppa:webupd8team/themes
sudo apt-get update
sudo apt-get install zukitwo-theme-all

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