Strobe

<html><head>
<title>Strobe</title>

<script>
<!-- If you're extremely unlucky, you may break your equipment, or worse, have a seizure -->
function toggleBgColor()
{
  document.bgColor = document.bgColor == '#ffffff' ? '#000000' : '#ffffff';
  setTimeout('toggleBgColor()', 200); //in milliseconds
}
</script>
</head>

<body onLoad='toggleBgColor();'>
</body></html>