There are several faces speedbar generates to provide a consistent color scheme across display types. You can customize these faces using your favorite method. They are:
You can also customize speedbar's initial frame parameters. How this is accomplished is dependent on your platform being Emacs or XEmacs.
In Emacs, change the alist
speedbar-frame-parameters. This variable is used to
set up initial details. Height is also automatically added when
speedbar is created, though you can override it.
In XEmacs, change the plist
speedbar-frame-plist. This is the XEmacs way of
doing the same thing.