Can't change the layout border color

I'm doing a simple Swing layout (see image) but for some reason no matter what I try I cannot change the colors of the 'borders' that split the three sections of the UI. Am I missing something?

The layout is done using GroupLayout.

EDIT:

The green portions are each individual JPanels contained within a GroupLayout.

I have tried background, and foreground colors, on any objects where it would make sense. I have tried applying EmptyBorder to each of the jpanels and still no luck. I think it might have to do with the layout but I'm not even sure about that.

Here is the relevent layout code. Note that this was all auto-generated by Netbeans:

    javax.swing.GroupLayout pnlTopLayout = new javax.swing.GroupLayout(pnlTop);
        pnlTop.setLayout(pnlTopLayout);
        pnlTopLayout.setHorizontalGroup(
            pnlTopLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 532, Short.MAX_VALUE)
        );
        pnlTopLayout.setVerticalGroup(
            pnlTopLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 59, Short.MAX_VALUE)
        );

javax.swing.GroupLayout pnlSideLayout = new javax.swing.GroupLayout(pnlSide);
        pnlSide.setLayout(pnlSideLayout);
        pnlSideLayout.setHorizontalGroup(
            pnlSideLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 200, Short.MAX_VALUE)
        );
        pnlSideLayout.setVerticalGroup(
            pnlSideLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 214, Short.MAX_VALUE)
        );

javax.swing.GroupLayout pnlMainLayout = new javax.swing.GroupLayout(pnlMain);
        pnlMain.setLayout(pnlMainLayout);
        pnlMainLayout.setHorizontalGroup(
            pnlMainLayout.createParalle开发者_运维问答lGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 326, Short.MAX_VALUE)
        );
        pnlMainLayout.setVerticalGroup(
            pnlMainLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 214, Short.MAX_VALUE)
        );

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(pnlSide, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(pnlMain, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addComponent(pnlTop, javax.swing.GroupLayout.DEFAULT_SIZE, 532, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(pnlTop, javax.swing.GroupLayout.PREFERRED_SIZE, 59, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(pnlMain, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(pnlSide, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)))
        );

You should be setting the background color of either the container's content pane, or the JComponent that overlays it (e.g. JPanel).

public final class Demo {
    private static BufferedImage bi;
    
    public static void main(String[] args){
        try {
            loadImage();
            
            SwingUtilities.invokeLater(new Runnable(){
                @Override
                public void run() {
                    createAndShowGUI();             
                }
            });
        } catch (IOException e) {
            // handle exception
        }
    }
    
    private static void loadImage() throws IOException{
        bi = ImageIO.read(Demo.class.getResource("../resources/whitefro1.jpg"));
    }
    
    private static void createAndShowGUI(){
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        final JPanel panel = new JPanel();
        panel.setBackground(Color.BLUE.darker()); // here
        
        final JLabel labelOne = new JLabel();
        labelOne.setIcon(new ImageIcon(bi));
        final JLabel labelTwo = new JLabel();
        labelTwo.setIcon(new ImageIcon(bi));
        
        panel.add(labelOne);
        panel.add(labelTwo);
        frame.add(panel);       
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

As you can see, the area between is colored a darker shade of blue.