title: GtkWidget, change background color
body: <p>Sorry, I'm newbie in the Gtk, so it is may be the stupid question. 
  I use Gtk+ 3.0 and have this code</p>
  
  <pre><code>GtkWidget *widget;
  widget=gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 2);
  gtk_box_pack_start(GTK_BOX(widget), some_label, FALSE, FALSE, 0);
  </code></pre>
  
  <p>How can I change the background color of the widget? I'm trying that</p>
  
  <pre><code>GdkColor red = {0, 0xffff, 0x0000, 0x0000};
  gtk_widget_modify_bg(widget, GTK_STATE_NORMAL, &amp;red);
  </code></pre>
  
  <p>and some other examples, but no one of them worked for my case. </p>