It compiles and links, but is *completely* untested.  Feel free to
pound on it.

The idea is to do all color management (allocation, etc.) via a
GdkColorContext so that apps will be friendly to 8-bit displays.

GdkColorContext is supposed to work on all visual/depth combinations.
This support, however, is lacking from the rest of Gdk/Gtk.  I will
try to work on that.

 - Federico