You can subclass JToolTip to create a custom appearance etc, then subclass the control in question to override its public JToolTip createToolTip() method (inherited from JComponent) to return an instance of your customised JToolTip subclass.
UIManager.put("ToolTip.foreground", new ColorUIResource(Color.WHITE));
UIManager.put("ToolTip.font", new FontUIResource(Font.SANS_SERIF,Font.BOLD,16));
We can use to change fonts , fore groud, background and border without sub classing JToolTip...
Just Write before setting ToolTip for any component.