Fixing #46238 and other EelBackground boo-boos

[Federico Mena Quintero <federico ximian com>]

Hi,

It looks like EelBackground and its helper EelBackgroundStyle are very
keen on using hardcoded defaults when the Nautilus theme does not
specify a color for something.  It looks to me like they should default
to the current GTK+ theme's colors.

For example, backgrounds fall back to white via the call to
eel_gdk_color_parse_with_white_default() inside
eel_background_ensure_realized().

The intention is to be able to create Nautilus themes that follow the
GTK+ theme and thus can be made accessible (high contrast, etc.) easily
by just changing your global GTK+ theme.

The above changes are non-negotiable, as they are the right thing to do
:)

Now, my question is whether we should modify the "GNOME" theme in
Nautilus not to include hardcoded color specifications.  This would make
it plainly follow the GTK+ theme.  It will look bland, but consistent. 
Does anyone else think the GNOME theme in Nautilus should be the
default, and it should also just follow your current GTK+ theme?

  Federico