Кнопки, изменяющие цвет фона

Пример:

<html>
<head>
<title>Кнопки, изменяющие цвет фона </title>
<Script Language="JavaScript">
  var computed = false
  var decimal = 0
  function convert (entryform, from, to)
    {convertfrom = from.selectedIndex
     convertto = to.selectedIndex
     entryform.display.value = (entryform.input.value * from[convertfrom].value / to[convertto].value )}
  function addChar (input, character)
    {if((character=='.' && decimal=="0") || character!='.')
    {(input.value == "" || input.value == "0") ? input.value = character : input.value += character
       convert(input.form,input.form.measure1,input.form.measure2)
       computed = true
	if (character=='.')
		{decimal=1}}}
  function openVothcom()
    {window.open("","Display window","toolbar=no,directories=no,menubar=no");}
  function clear (form)
    {form.input.value = 0
     form.display.value = 0
     decimal=0}
  function changeBackground(hexNumber)
    {document.bgColor=hexNumber}
</Script>
</head>
<body bgcolor="333333" text="white" link="#FFFF99" alink="#FFFF99" vlink="#FFFF99">
<Form Method="POST" Name="background">
  <p align="center">
  <Input Type="button" Value="yellow" OnClick="changeBackground('#fff000')">
  <Input Type="button" Value="black" OnClick="changeBackground('#000000')">
  <Input Type="button" Value="white" OnClick="changeBackground('#ffffff')">
  <Input Type="button" Value="green" OnClick="changeBackground('#00ff00')">
  <Input Type="button" Value="blue" OnClick="changeBackground('#0000ff')">
  <Input Type="button" Value="orange" OnClick="changeBackground('#ff8000')">
  <Input Type="button" Value="gray" OnClick="changeBackground('#c0c0c0')">
  <Input Type="button" Value="red" OnClick="changeBackground('#ff0000')">
</Form>

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</body>
</html>