Mudar cor do Botão....

package testeSwing;

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;

public class MudaCorBotao extends JFrame {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	private JButton btn;

	private final Color C1 = Color.YELLOW, C2 = Color.GREEN;

	public MudaCorBotao() {
		super("Mudar cor do botão");
		setSize(300, 300);
		setDefaultCloseOperation(EXIT_ON_CLOSE);
		setLayout(null);
		

		add(btn = new JButton("Mudar Cor"));
		btn.setBackground(C1);
		btn.setBounds(5, 5, 100, 25);

		btn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent arg0) {
				//Se for a cor um, então mudo para a cor 2...
				btn.setBackground(btn.getBackground() == C1 ? C2 : C1);
			}
		});
		
		
	}

	public static void main(String[] args) {
		new MudaCorBotao().setVisible(true);
	}

}

package testeSwing;

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;

public class MudaCorBotao extends JFrame {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	private JButton btn;

	private final Color C1 = Color.YELLOW, C2 = Color.GREEN;

	public MudaCorBotao() {
		super("Mudar cor do botão");
		setSize(300, 300);
		setDefaultCloseOperation(EXIT_ON_CLOSE);
		setLayout(null);
		

		add(btn = new JButton("Mudar Cor"));
		btn.setBackground(C1);
		btn.setBounds(5, 5, 100, 25);

		btn.addActionListener(new ActionListener() {

			@Override
			public void actionPerformed(ActionEvent arg0) {
				//Se for a cor um, então mudo para a cor 2...
				btn.setBackground(btn.getBackground() == C1 ? C2 : C1);
			}
		});
		
		
	}

	public static void main(String[] args) {
		new MudaCorBotao().setVisible(true);
	}

}