Redraw TreeView

If I want a TreeNode give a new image:

   if TreeView.Selected.ImageIndex = itemRedButton then
     TreeView.Selected.ImageIndex := itemGreenButton
   else
     TreeView.Selected.ImageIndex := itemRedButton;
   TreeView.Selected.SelectedIndex := TreeView.Selected.ImageIndex;

I have to flip the StateIndex to force the TreeView to redraw:

   TreeView.Selected.StateIndex := -1;
   TreeView.Selected.StateIndex := itemCheckBoxFalse;

What am I doing wrong ?

Thanks,
Fons.