test.html
<IFRAME ID="frame1" SRC="a.html" allowTransparency="true" HEIGHT=180 WIDTH=300>
</IFRAME>
<IFRAME ID="frame2" SRC="b.html" allowTransparency="true"
STYLE="background-color:#459800" HEIGHT=180 WIDTH=300>
</IFRAME>
按钮定义如下：
<INPUT TYPE="button" VALUE="不透明" onclick="turnTransparencyOff()">
<INPUT TYPE="button" VALUE="透明" onclick="turnTransparencyOn()">
<script>
//函数turnTransparencyOff()：
function turnTransparencyOff()
{ document.all.frame1.allowTransparency = false;
document.all.frame2.allowTransparency = false; }
//函数turnTransparencyOn()：
function turnTransparencyOn()
{ document.all.frame1.allowTransparency = true;
document.all.frame2.allowTransparency = true; }
</script></SPAN>
a.html
<HTML><HEAD><TITLE></TITLE>
<META http-equiv=Content-Type content="text/html; charset=gb2312">
</HEAD>
<BODY style="BACKGROUND-COLOR: transparent">
<H1>透明文档</H1>
此IFRAME无背景颜色
BODY：
</BODY></HTML>
b.html
<HTML><HEAD><TITLE></TITLE>
<META http-equiv=Content-Type content="text/html; charset=gb2312">
</HEAD>
<BODY style="BACKGROUND-COLOR: transparent">
<H1>透明文档</H1>
此IFRAME有背景颜色
BODY：
</BODY></HTML>