This is the best little snippet you'll ever see on this site, maybe. . . depends on how many years this site will be around, it's going pretty good right now, but anyway this snippet will make it so when you select the colour(color if you're American which I'm not) out of a drop down menu, it will change all the tables, and if you know how to make a web site then you know all you use are tables so it will pretty much change the background, well here it is F.Y.I. I'm kinda reluctant to give this away, this is ingenious, and even if the person leaves the site and comes back later, it will stay the same!
P.S. It's long, kinda like this description :)
P.S.S. I know there is a bit of unecessary stuff there but it's worth it ;)

<? @session_start(); 
$_SESSION['color']=$_POST['col']; 
$_SESSION['sel']=$_POST['inp']; 
$_SESSION['inp']=$_POST['inp'];
$_SESSION['text']=$_POST['tex']; 
?>
<? @session_start(1); 
$_SESSION['color']=$_POST['col']; 
$_SESSION['sel']=$_POST['inp']; 
$_SESSION['inp']=$_POST['inp']; 
$_SESSION['text']=$_POST['tex']; 
?>

<style type="text/css"> 
<!-- 
table { 
    background-color: <? if($_SESSION['color']!='') echo $_SESSION['color']; else echo '#999900'; ?> 
} 
td { 
    font-family: Verdana, Arial, Helvetica, sans-serif; 
    font-size: 12px; 
    font-weight: bolder; 
    color: #CCFF66; 
} 
font {

}
input { 
    background-color:<? if($_SESSION['inp']!='') echo $_SESSION['inp']; else echo '#663399'; ?> 
    font-family: Verdana, Arial, Helvetica, sans-serif; 
    font-size: 12px; 
    color: #FF0000; 
} 
select { 
    font-family: Verdana, Arial, Helvetica, sans-serif; 
    font-size: 12px; 
    color: #FFFFFF; 
    background-color:<? if($_SESSION['sel']!='') echo $_SESSION['sel']; else echo '#669999'; ?> 
} 
--> 
</style> 

<?
echo 'Banner color: ',$_POST['col']; 

?>
<br>
<form name="form1"  method="post" > 

      <?php    

function makeSelectMenu($menuName, $options, $chosen) { 
    $list = ''; 
    foreach ($options as $option => $text) { 
        $selected = ($chosen === $option) ? ' selected="selected"' : ''; 
        $list .= " <option value=\"$option\"$selected>$text</option>\n"; 
    } 
    return "\n<select name=\"$menuName\" id=\"$menuName\">\n$list</select>\n"; 
} 

session_start(); 

$options = array( 
'#336600' => '#336600 Dark Green', 
'#999966' => '#999966 Light Brown' ,
'#669966' => '#669966 Light Green' ,
'#ef5966' => '#ef5966 Pink',
'#3366ff' => '#3366ff Blue',
'#ff6600' => '#ff6600 Orange' ,
'#339900' => '#339900 Green' ,
'#335566' => '#335566 Navy' ,
'#66f9ff' => '#66f9ff Aqua' ,
'#efdf66' => '#efdf66 Mustard' ,
'#fd66ff' => '#fd66ff Fuscia' ,
'#ff66cc' => '#ff66cc Rose'
  ); 
  $menuName = 'col';
  if (isSet($_POST[$menuName])) { 
    $_SESSION[$menuName] = $_POST[$menuName]; 
} 

if (isSet($_SESSION[$menuName])) { 
    $chosen = $_SESSION[$menuName]; 
} else { 
    $chosen = ''; 
} 

$selectMenu = makeSelectMenu($menuName, $options, $chosen);  

?>

<?
$options = array( 
'' => 'Choose the Background',
'#336600' => '#336600 Dark Green', 
'#999966' => '#999966 Light Brown' ,
'#669966' => '#669966 Light Green' ,
'#ef5966' => '#ef5966 Pink',
'#3366ff' => '#3366ff Blue',
'#ff6600' => '#ff6600 Orange' ,
'#339900' => '#339900 Green' ,
'#335566' => '#335566 Navy' ,
'#66f9ff' => '#66f9ff Aqua' ,
'#efdf66' => '#efdf66 Mustard' ,
'#fd66ff' => '#fd66ff Fuscia' ,
'#ff66cc' => '#ff66cc Rose'
  ); 
    $menuName = 'col'; 
$chosen = ''; 
if (isSet($_POST[$menuName])) $_SESSION[$menuName] = $_POST[$menuName]; 
if (isSet($_SESSION[$menuName])) $chosen = $_SESSION[$menuName]; 
$selectMenu = makeSelectMenu($menuName, $options, $chosen); 

?> 

<form method="post"> 

<?php echo $selectMenu; ?> 

    <?php    

function makeSelectMenu1($menuName1, $options1, $chosen1) { 
    $list1 = ''; 
    foreach ($options1 as $option1 => $text1) { 
        $selected1 = ($chosen1 === $option1) ? ' selected="selected"' : ''; 
        $list1 .= " <option value=\"$option1\"$selected1>$text1</option>\n"; 
    } 
    return "\n<select name=\"$menuName1\" id=\"$menuName1\">\n$list1</select>\n"; 
} 

session_start(1); 

    $options1 = array( 
'' => 'Choose the Background',
'#336600' => '#336600 Dark Green', 
'#999966' => '#999966 Light Brown' ,
'#669966' => '#669966 Light Green' ,
'#ef5966' => '#ef5966 Pink',
'#3366ff' => '#3366ff Blue',
'#ff6600' => '#ff6600 Orange' ,
'#339900' => '#339900 Green' ,
'#335566' => '#335566 Navy' ,
'#66f9ff' => '#66f9ff Aqua' ,
'#efdf66' => '#efdf66 Mustard' ,
'#fd66ff' => '#fd66ff Fuscia' ,
'#ff66cc' => '#ff66cc Rose'
  ); 
    $menuName1 = 'inp'; 

if (isSet($_POST[$menuName1])) { 
    $_SESSION[$menuName1] = $_POST[$menuName1]; 
} 

if (isSet($_SESSION[$menuName1])) { 
    $chosen1 = $_SESSION[$menuName1]; 
} else { 
    $chosen1 = ''; 
} 

$selectMenu1 = makeSelectMenu1($menuName1, $options1, $chosen1);  

    $options1 = array( 
'#336600' => '#336600 Dark Green', 
'#999966' => '#999966 Light Brown' ,
'#669966' => '#669966 Light Green' ,
'#ef5966' => '#ef5966 Pink',
'#3366ff' => '#3366ff Blue',
'#ff6600' => '#ff6600 Orange' ,
'#339900' => '#339900 Green' ,
'#335566' => '#335566 Navy' ,
'#66f9ff' => '#66f9ff Aqua' ,
'#efdf66' => '#efdf66 Mustard' ,
'#fd66ff' => '#fd66ff Fuscia' ,
'#ff66cc' => '#ff66cc Rose'
  );

    $menuName1 = 'inp'; 
$chosen1 = ''; 
if (isSet($_POST[$menuName1])) $_SESSION[$menuName1] = $_POST[$menuName1]; 
if (isSet($_SESSION[$menuName1])) $chosen1 = $_SESSION[$menuName1]; 
$selectMenu1 = makeSelectMenu1($menuName1, $options1, $chosen1); 

?> 

<form method="post"> 

<?php echo $selectMenu1; ?> 

      <input type="submit" name="Submit" value="Submit">

</form>