#color1,#color2,#color3{border:5px #FFFFFF solid;width:30px; height:30px}
#color1{ background:#FF9900;}
#color2{ background:#00CCFF;}
#color3{ background:#000000;}
</style>
<script>
function colors(i)
{
if(i==1)
bodys.style.background="#FF9900";
else if(i==2)
bodys.style.background="#00CCFF";
else
bodys.style.background="#000";
}
</script>
<body id="bodys">
<input type="button" id="color1" onclick="colors(1)">
<input type="button" id="color2" onclick="colors(2)">
<input type="button" id="color3" onclick="colors(3)">
</body>
效果達到了!