How to Set a Jlabel's Background Color

How do I set a JLabel's background color?

Use

label.setOpaque(true);

Otherwise the background is not painted, since the default of opaque is false for JLabel.

From the JavaDocs:

If true the component paints every pixel within its bounds. Otherwise, the component may not paint some or all of its pixels, allowing the underlying pixels to show through.

For more information, read the Java Tutorial How to Use Labels.

JLabel.setBackground(Color color) doesn't work?

A component must be opaque for its background do be effective, a JLabel's default is false, so you have to set it:

label.setOpaque(true);

Java JLabel background color not working?

I'm having trouble getting the JLabel to have a background color whilst the JPanel is white

You need to call setOpaque(true); in your JLabel

Also, is there a way to resize the JPanel to half of what the JFrame is?

You could use a GridLayout, and place 2 JPanels in it, that way, you're going to have 2 JPanels using half the size of your JFrame each.

Also, rename your classes, Panel belongs to the name of a class in AWT, same for Frame and Label, this might confuse your (and whoever reads your code).

Never extend JFrame, instead build your GUI based on JPanels. See extends JFrame vs creating it inside of class and The use of multiple JFrames, Good / Bad practice? The general consensus says it's bad.

Also you should also check Should I avoid the use of setPreferred|Maximum|MinimumSize() in Swing? Again, yes, you should and instead override the getPreferredSize() method.

Don't forget to place your program on the Event Dispatch Thread (EDT) by changing your main() method as follows:

public static void main(String[] args) {
    //Java 8 with lambda expressions
    SwingUtilities.invokeLater(() -> 
        //Your code here
    );
    //Java 7 and below (Or 8 without lambda expressions)
    SwingUtilities.invokeLater(new Runnable() {
        //Your code here
    });
}

Now, with all the above recommendations, your code should now look like this:

import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridLayout;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class HalfSizePanelWithLabelInDifferentColor {

    private JFrame frame;
    private Container contentPane;
    private JPanel pane;
    private JPanel pane2;
    private JLabel label;

    private static final Dimension dim = new Dimension(100, 100);

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new HalfSizePanelWithLabelInDifferentColor().createAndShowGui());
    }

    public void createAndShowGui() {
        frame = new JFrame(getClass().getSimpleName());

        contentPane = frame.getContentPane();
        pane = new JPanel() {
            @Override
            public Dimension getPreferredSize() {
                return dim;
            }
        };

        pane2 = new JPanel();

        pane.setOpaque(false);
        pane2.setOpaque(false);

        pane.setBorder(BorderFactory.createLineBorder(Color.RED));
        pane2.setBorder(BorderFactory.createLineBorder(Color.BLUE));

        label = new JLabel("Hello World!");
        label.setBackground(Color.GREEN);
        label.setOpaque(true);

        contentPane.setLayout(new GridLayout(2, 1));

        pane.add(label);

        contentPane.add(pane);
        contentPane.add(pane2);

        contentPane.setBackground(Color.WHITE);

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

And your output would be like this:

Sample Image

Note that I added some colored borders to show where a pane starts and ends and where the other one starts and ends

how to set color of multiple jlabel on click netbeans?

You could simply need to:

Create 1 method which will handle what happens to a JLabel when clicked.
Use the JPanel's .getComponents() to get all the components.
Use the instance of operator to ensure that the component is a JLabel.
If the component is a JLabel, assign the method in 1 as the click event handler.

In the event handler, then, simply do the same as above. The event itself should give you access to the source, that is the component which triggered the event. You would simply need to do as follows:

Iterate over the labels and set them to a green background.*
Take the source of the event and set it to red.

*This can be improved by keeping a label which denotes the currently selected label. When a label is clicked, you would reset the background of that label and update it to show the new label which the user has clicked.

How to change JLabel background when I click the JLabel in Java

By default a JLabel is non-opaque so its background is not painted. You need to make the label opaque when you create it:

lblKembali = new JLabel("Kembali");
lblKembali.setOpaque( true );

Also you can make your listener more generic so it can be shared by multiple components by doing:

public void mouseClicked(MouseEvent e) 
{
    Component c = e.getComponent();
    c.setBackground(Color.BLUE);
}

How to change JLabel's background color through mouse events?

e.getSource() will return the label that is clicked, not the color of that label (in your example, anyway)

So, cast to a label:

JLabel theLabel = (JLabel) e.getSource();

then setBackground on it appropriately:

if (theLabel.getBackground().equals(Color.WHITE)) theLabel.setBackgound(...);

Java JLabel background color cant be changed using Netbeans

You'd need to set opaque to true

yourLabel.setOpaque(true);

(Or tick the opaque box in the label's properties in design view in NetBeans)