How to delete grey borders

[lnplnp]

    import com.smartgwt.client.widgets.layout.HLayout;
    import com.smartgwt.client.widgets.tree.TreeGrid;

    HLayout layout = new HLayout();
    TreeGrid treeGrid = new TreeGrid();

    layout.setMembersMargin(0);
    layout.setBorder("0 none");
    layout.setPaddingAsLayoutMargin(false);
    layout.setLayoutMargin(0);
    layout.setCanDragResize(false);
    for (Canvas canvas : layout.getMembers()) {
      canvas.setMargin(0);
      canvas.setPadding(0);
      canvas.setBorder("0 none");
      canvas.setWidth("100%");
      canvas.setHeight("100%");
    }
    treeGrid.setMargin(0);
    treeGrid.setBorder("0 none");

I have try all these methods and border are still around the treeGrid which is in 'layout'.

How to delete or tell GWT to do not generate these grey borders we can see between blue and green borders ?

Or is there a component which is without these borders ?