System Tools | Preferences - Advanced Preferences - been a while since I looked!
You can also:
1. Install gnome tweak-tool from a terminal (Ctrl+ Alt+ T):
- Code:
sudo apt-get install gnome tweak-tool
2. Change the way your panel looks:
right-click panel and select preferences, go to last tab and change the box settings to get a gradation effect on your panel by choosing the colours of your choice.
3. Install Ubuntu-tweak from the official site:
http://ubuntu-tweak.com/4. Install 'gnome-color-chooser':
- Code:
sudo apt-get install gnome-color-chooser
5. Install 'Gtk.Ch' (change themes):
Menu | System Tools | Administration | Synaptic Package Manager
Search for Gtk theme changer.
6. Search for Gizmuntu's uploads on this forum for differently coloured Win7 Menus and AWN panels.

7. Play around with Compiz Settings - you can change the Top and Bottom of the cube with wallpapers of your choice if you wish!