md5flag.php

<?php

$thing = $_GET['thing'];

$md5 = md5($thing);

$col1 = substr($md5, 0, 6);
$col2 = substr($md5, 6, 6);
$col3 = substr($md5, 12, 6);

echo
    "<div style='float:left;width:100px;height:200px;background:#{$col1}'></div>\n" .
    "<div style='float:left;width:100px;height:200px;background:#{$col2}'></div>\n" 
    "<div style='float:left;width:100px;height:200px;background:#{$col3}'></div>";