Java GUI - JOptionPane/JDialog customization issue

问题

So I'm trying to make a simple dialog where the user can input some information... My problem is that I'm trying to make the whole background white; I got MOST of it, but there's a gray line behind the buttons that I don't know how to fix (make white as well). How can I fix it? :(

What it looks like:

What I want:

Code:

JPanel all = new JPanel();
all.setLayout(new BorderLayout());
all.add(names, BorderLayout.NORTH);
all.add(academic, BorderLayout.CENTER);
all.setBackground(Color.WHITE);
all.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20)); //int top, int left, int bottom, int right

Object [] options = {"SAVE", "EXIT"};
JOptionPane jop = new JOptionPane(all, JOptionPane.PLAIN_MESSAGE , JOptionPane.YES_NO_OPTION, null, options, null);
final JDialog dialog = jop.createDialog(null, "Username Information");
jop.setBackground(Color.WHITE);
dialog.setBackground(Color.WHITE);
dialog.setLocation(585, 300);
dialog.setVisible(true);
String choice = (String) jop.getValue();

来源：https://stackoverflow.com/questions/29785580/java-gui-joptionpane-jdialog-customization-issue