Gadget de mudar background

Resultado 1
Resultado 2

1. Vá ao painel do blog > Layout > Adicionar gadget
2. Escolha a opção HTML/JavaScript
Para o resultado 1, cole:
<div style="text-align:center;"></div><br /><center>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#ff0000'; document.body.style.backgroundImage='none';"><img src="http://4.bp.blogspot.com/_dsEG33PDaHw/S32TTX4H60I/AAAAAAAAAJU/qYc4BYZclgg/s200/body-rojo.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#fff000'; document.body.style.backgroundImage='none';"><img src="http://2.bp.blogspot.com/_dsEG33PDaHw/S32TK7730eI/AAAAAAAAAIs/3v5O2GDrs1s/s200/body-amarillo.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#04B404'; document.body.style.backgroundImage='none';"><img src="http://2.bp.blogspot.com/_dsEG33PDaHw/S32TTyfDggI/AAAAAAAAAJk/9x17-Ec7Dnw/s200/body-verde.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#0080FF'; document.body.style.backgroundImage='none';"><img src="http://4.bp.blogspot.com/_dsEG33PDaHw/S32TLXeztWI/AAAAAAAAAI0/7hWfrfWsdKU/s200/body-azul.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#CC00FF'; document.body.style.backgroundImage='none';"><img src="http://2.bp.blogspot.com/_dsEG33PDaHw/S32TMB5SOXI/AAAAAAAAAJE/PRMfKVBj6fM/s200/body-morado.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#F781BE'; document.body.style.backgroundImage='none';"><img src="http://1.bp.blogspot.com/_dsEG33PDaHw/S32TTl7vW9I/AAAAAAAAAJc/GHdXgYyF4Ro/s200/body-rosa.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#000000'; document.body.style.backgroundImage='none';"><img src="http://2.bp.blogspot.com/_dsEG33PDaHw/S32TMY3FA9I/AAAAAAAAAJM/6Hx0CAagVOQ/s200/body-negro.png" /></a>
<a href="#" onclick="javascript:document.body.style.backgroundColor='#FFFFFF'; document.body.style.backgroundImage='none';"><img src="http://2.bp.blogspot.com/_dsEG33PDaHw/S32TLuZ0f1I/AAAAAAAAAI8/r1AHB4GpoPQ/s200/body-blanco.png" /></a>
</center>
Para o resultado 2, cole:
 <div class='widget HTML' id='HTML7'>
<h2 class='title'></h2>
<div class='widget-content'>
<style>
#backgrounds a img{
width:40px;
height:40px;
display:inline;
margin-right:10px;
margin-top:15px;
border:2px solid #FFFFFF;
}
#backgrounds a:hover img{
border:2px solid #FFEC8B;
}
</style>
<div id="backgrounds">
<script src='http://code.jquery.com/jquery-1.6.2.min.js' type='text/javascript'></script>
<script>
$(document).ready(function(){
 $("#background01").click(function(){
$("body").css({"background":"url(URLDOFUNDO1)"});
 });
});
$(document).ready(function(){
 $("#background02").click(function(){
$("body").css({"background":"url(URLDOFUNDO2)"});
 });
});
$(document).ready(function(){
 $("#background03").click(function(){
$("body").css({"background":"url(URLDOFUNDO3)"});
 });
});
</script>
<center><a href="javascript:void(O)" id='background01' title="1"><img src="URLDOFUNDO1" /></a>
<a href="javascript:void(O)" id='background02' title="2"><img src="URLDOFUNDO2" /></a>
<a href="javascript:void(O)" id='background03' title="3"><img src="URLDOFUNDO3" /></a></center></div>
</div></div>

Substitua os trechos em vermelho pelo background 1, os trechos em rosa pelo background 2 e os trechos em azul pelo background 3.

3. Salve.