An Highlighting example

Test.java

package test;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Test {
    
    private static Color[] colors = new Color[]{Color.RED, Color.GREEN, Color.CYAN, Color.MAGENTA, Color.BLACK, Color.BLUE};
    private static Random rnd = new Random();
    
    public static void main(String[] args){
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(640, 480);
        
        final JPanel panel = new JPanel();
        panel.setBackground(colors[colors.length - 1]);
        panel.setPreferredSize(new Dimension(400, 400));

        final JButton btn = new JButton("ClickMe");
        btn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                ComponentHighlighter highlighter = new ComponentHighlighter(panel, colors[rnd.nextInt(colors.length - 1)]);
                highlighter.start();
            }
        });
        panel.add(btn);
        
        f.getContentPane().add(panel);
        f.pack();
        f.setVisible(true);
    }
    
    private static class ComponentHighlighter extends Timer implements ActionListener{
        private Color backgroundEndColor;
        private Color backgroundStartColor;
        private Color backgroundColor;

        private int step = 0;
        private int maxSteps = 30;
        
        private final JComponent comp;
        
        public ComponentHighlighter(JComponent panel, Color highlightColor) {
            super(1000/30, null);
            
            addActionListener(this);

            this.comp = panel;
            backgroundStartColor = highlightColor;
            backgroundEndColor = panel.getBackground();
            backgroundColor = backgroundStartColor;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            if(step >= maxSteps){
                this.stop();
                comp.setBackground(backgroundEndColor);
                return;
            }
            backgroundColor = interpolateCurrentColor();
            comp.setBackground(backgroundColor);
            step++;
        }
        
        private Color interpolateCurrentColor(){
            return new Color(
                backgroundStartColor.getRed() + ((step * (backgroundEndColor.getRed() - backgroundStartColor.getRed())) / (maxSteps - 1)), 
                backgroundStartColor.getGreen() + ((step * (backgroundEndColor.getGreen() - backgroundStartColor.getGreen())) / (maxSteps - 1)), 
                backgroundStartColor.getBlue() + ((step * (backgroundEndColor.getBlue() - backgroundStartColor.getBlue())) / (maxSteps - 1)), 
                backgroundStartColor.getAlpha() + ((step * (backgroundEndColor.getAlpha() - backgroundStartColor.getAlpha())) / (maxSteps - 1))
            );
        }
    }
}