$(document).ready(function(){
    var src= $('img#mainImage').attr('src');
    
    $('a.altColor').bind("mouseenter",function(){
        $('img#mainImage').attr('src',this.href);
    }).bind("mouseleave",function(){
        $('img#mainImage').attr('src',src);
    });
    
    $('a.altColor').click(function(event){
        event.preventDefault();
    });
});