Spectrum is a Gnome project by Paper-On-Fire that provides more than hundred panel backgrounds, which have top and bottom variations and two different sizes, 26 pixels and 36 pixels. Spectrum also includes Dingo source files and all the icons from Pictobit:

- A few custom Chromo Erectus icons (folder-icons and DOSBox-icon)
- A DOSBox icon that is the same style as the ScummVM icon
- Three DOSBoxGL icons
- Horizon: OpenOffice and VirtualBox icons
- Simple: OpenOffice and Virtual Box icons
- My custom Gnome-menu icon

To use the background, download and extract Spectrum from here. Right-click on panel and select Properties choose an image file under Background tab.

- How to use most backgrounds with vertical panels:
1. Open gconf-editor.
2. Open “apps”, then “panel” and then “toplevels”.
3. Open the panel’s folder that you want to customize, and open “background”.
4. Check rotate and fit and close gconf-editor.
6. Right-click the panel and select panel options, and open the background tab.
7. Select the background image you want to use.
To change the background again, repeat steps 6 and 7.

Links: http://paper-on-fire.deviantart.com/