added the possibility to change docking area background

dockinginfonode/src/main/java/fr/soleil/docking/infonode/InfoNodeDockingManager.java

@@ -66,6 +66,14 @@ public class InfoNodeDockingManager extends ADockingManager {
         return result;
     }
 
+    @Override
+    public void setDockingAreaBeackground(JComponent dockingArea, Color areaBackground) {
+        if (dockingArea instanceof RootWindow) {
+            RootWindow rootWindow = (RootWindow) dockingArea;
+            rootWindow.getRootWindowProperties().getWindowAreaProperties().setBackgroundColor(areaBackground);
+        }
+    }
+
     @Override
     public void loadPerspective(IPerspective perspective) throws DockingException {
         DockingException dockingException = null;