是否可以将垂直制表符设置为具有透明背景

I have a tabbed pane setup and set to the left so that the tabs go from top to bottom. unfortunately, the unused space is an ugly gray color. im having trouble setting that to be completely transparent. This combined with the setUndercorated(true) for the parent frame, it should have the effect of hanging over the window. how do i set it to transparent?I have a tabbed pane setup and set to the left