Steps to reproduce:
The following test case crashes:

import org.gnu.gdk.Color;
import org.gnu.gtk.Gtk;

public class ColorTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Gtk.init(args);
		
		Color c = new Color(0,0,0);
		System.gc();
		Gtk.main();
	}
}

Stack trace:
Could not generate a stack trace, but the following message is displayed:
Gdk-ERROR **: file gdkcolor.c: line 145 (gdk_color_free): assertion failed:
(color_chunk != NULL)

Other information: