I'm using following gtkrc to make the text cursor more strongly rendered:

  style "default"
  {
     GtkWidget::cursor-aspect-ratio = 1.0
  }
  class "GtkWidget" style "default"
  gtk-cursor-blink = 0

However, this setting is not useful: the characters under the cursor
is hidden by the fat cursor itself. The fat cursor may be one of general
requirements from shortsighted users.

Here is the patch:

2006-07-13  Masatake YAMATO  <jet@gyve.org>

	* gtk/gtkstyle.c (make_cursor_gc): Set GDK_NOR to cursor's gc.function.

Index: gtkstyle.c
===================================================================
RCS file: /cvs/gnome/gtk+/gtk/gtkstyle.c,v
retrieving revision 1.194
diff -u -r1.194 gtkstyle.c
--- gtkstyle.c	6 Jul 2006 05:14:02 -0000	1.194
+++ gtkstyle.c	13 Jul 2006 08:07:56 -0000
@@ -6576,7 +6576,10 @@
     }
   else
     gc_values.foreground = *fallback;
-  
+
+  gc_values_mask |= GDK_GC_FUNCTION;
+  gc_values.function = GDK_NOR;
+
   gdk_rgb_find_color (widget->style->colormap, &gc_values.foreground);
   return gtk_gc_get (widget->style->depth, widget->style->colormap, &gc_values, gc_values_mask);
 }