You could make a ".gtkrc-2.0" file and place it in your /home/user directory like this:
~/.gtkrc-2.0
Check this thread out where I showed how to make one with a custom image:
[link]Just make your custom .png image only 1 pixel wide and as tall as you want your panel (like 30 pixels).
This is the only code you would need in your ~.gtkrc-2.0:
--------------------------------
style "panel"
{
bg[NORMAL] = "#181818"
bg_pixmap[NORMAL] = "1wx30h-image.png"
fg[NORMAL] = "#FFFFFF"
}
widget_class "*Panel*" style "panel"
widget "*Panel*" style "panel"
class "*Panel*" style "panel"
---------------------------------
or if you don't want to use an image, just make it like this:
---------------------------------
style "panel"
{
bg[NORMAL] = "#181818"
fg[NORMAL] = "#FFFFFF"
}
widget_class "*Panel*" style "panel"
widget "*Panel*" style "panel"
class "*Panel*" style "panel"
--------------------------------
The bg[NORMAL] = "#181818" will be the panel color.
And the fg[NORMAL] = "#FFFFFF" will be the font color.