colorize = function (id) {
    o = document.getElementById(id.id);    
    s=o.src
    if(s.indexOf('_a')>0) {
        s = s.replace(/_a/, "");
    }
    else{
        s = s.replace(/.jpg/, "_a.jpg");
    }
    im =new Image;
    im.src = s;    
    o.src=im.src;    
}