Inverse Hex Color

<?php
/**
 * Inverses a provided hex color. If you pass a hex string with a 
 * hash(#), the function will return a string with a hash prepended
 * @param string $color Hex color to flip
 * @return string Reversed hex color
 * @author Koncept
 * 
 * Last Update: 2008-10-05
 */
function inverseHex( $color )
{
	$color       = trim($color);
	$prependHash = FALSE;
 
	if(strpos($color,'#')!==FALSE) {
		$prependHash = TRUE;
		$color       = str_replace('#',NULL,$color);
	}
 
	switch($len=strlen($color)) {
		case 3:
			$color=preg_replace("/(.)(.)(.)/","\\1\\1\\2\\2\\3\\3",$color);
			break;
		case 6:
			break;
		default:
			trigger_error("Invalid hex length ($len). Must be a minimum length of (3) or maxium of (6) characters", E_USER_ERROR);
	}
 
	if(!preg_match('/^[a-f0-9]{6}$/i',$color)) {
		$color = htmlentities($color);
		trigger_error( "Invalid hex string #$color", E_USER_ERROR );
	}
 
	$r = dechex(255-hexdec(substr($color,0,2)));
	$r = (strlen($r)>1)?$r:'0'.$r;
	$g = dechex(255-hexdec(substr($color,2,2)));
	$g = (strlen($g)>1)?$g:'0'.$g;
	$b = dechex(255-hexdec(substr($color,4,2)));
	$b = (strlen($b)>1)?$b:'0'.$b;
 
	return ($prependHash?'#':NULL).$r.$g.$b;
}
 
// Demo
echo inverseHex('#000000'); // #ffffff
?>