Hola
Lo que hacen en este caso es que el que tiene el color como difuso ess una imagen igual a la que se muestra
yu por medio de javascript estan intercambiando el src entre la imagen difusa y la que no
Este es el coddigo de la pagina
<div id="thumbnail_2">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/0.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/0.jpg" id="0">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/1.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/1.jpg" id="1">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/2.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/2.jpg" id="2">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/3.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/3.jpg" id="3">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/4.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/4.jpg" id="4">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/5.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/5.jpg" id="5">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/6.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/6.jpg" id="6">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/7.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/7.jpg" id="7">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/8.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/8.jpg" id="8">
<img onmouseout="this.src='../commercial_1/images/thumnails_top/light/9.jpg'" onmouseover="return replace_with_dark_image(this.id, '../commercial_1/')" src="http://www.forosdelweb.com/f16/commercial_1/images/thumnails_top/light/9.jpg" id="9">
</div>
Y esta function de javascript cambia la iamgen grande
function replace_with_dark_image(id, dir) {
document.getElementById('main_wide_photo').style.d isplay = 'none'
document.getElementById('main_photo').style.displa y = 'block'
document.getElementById(id).src = dir + '/images/thumnails_top/' + id + '.jpg';
document.getElementById('photo').src = dir + '/images/big_images/' + id + '.jpg'
}
espero que te sirva