Edit in JSFiddle

var rect;
var rect2;

window.onload = function(){
    var paper = Raphael(0,0,"100%","100%");
    rect = paper.rect(0,0,100,100)
        .attr({fill:"#400"});
    rect2 = paper.rect(50,50,100,100)
        .attr({fill:"#808"});
}
    

    function hide(){
        //紫を後ろに
        rect2.hide();
    }
    
    function show(){
        //紫を前に
        rect2.show();
    }

<script type="text/javascript" src="http://dl.dropbox.com/u/63305355/raphael-min.js"></script>
<div id="canvas">
    <div class="text">
        HIDE/SHOW
        <input type="button" value="Hide" onclick="hide()" />
        <input type="button" value="Show" onclick="show()" />
    </div>
</div>

body,html
{
    height:100%;
    margin:0;
}

#canvas 
{
    height:99%;
    background:#ccc;
    text-align:center;
}

.text{
    letter-spacing: 20px;
    color:#fff;
    font-size:150%;
    width:60%;
    height:60%;
    position:absolute;
    left:20%;
    top:40%;
    z-index:1;
}