php color manipulation

color.php

<?php

function hex2rgb( $col ) {
	if ( $col[0] == '#' ) {
		$col = substr( $col, 1 );
	}
	if (strlen( $col ) == 6) {
		list( $r, $g, $b ) = array( $col[0] . $col[1], $col[2] . $col[3], $col[4] . $col[5] );
	} elseif (strlen( $col ) == 3) {
		list( $r, $g, $b ) = array( $col[0] . $col[0], $col[1] . $col[1], $col[2] . $col[2] );
	} else {
		return false;
	}
	$r = hexdec( $r );
	$g = hexdec( $g );
	$b = hexdec( $b );
	return array($r, $g, $b);
}

function hex2rgba( $hex, $a ) {
	$arr = hex2rgb($hex);
	$str = "rgba($arr[0],$arr[1],$arr[2],$a)";
	return $str;
}

function rgb2hex( $arr ) {
	$new = array();
	$new[0] = (string) dechex($arr[0]);
	$new[1] = (string) dechex($arr[1]);
	$new[2] = (string) dechex($arr[2]);
	foreach($new as $k => $v) {
		if (strlen($v) === 1)
			$new[$k] = "0$v";
	}
	return '#' . $new[0] . $new[1] . $new[2];
}

function darken( $hex, $steps ) {
	$arr = hex2rgb($hex);
	$r = max(0, min(255,$arr[0] - $steps) );
	$g = max(0, min(255,$arr[1] - $steps) );  
	$b = max(0, min(255,$arr[2] - $steps) );
	$rgb = array($r,$g,$b);
	return rgb2hex($rgb);
}

function lighten( $hex, $steps ) {
	$arr = hex2rgb($hex);
	$r = max(0, min(255,$arr[0] + $steps) );
	$g = max(0, min(255,$arr[1] + $steps) );  
	$b = max(0, min(255,$arr[2] + $steps) );
	$rgb = array($r,$g,$b);
	return rgb2hex($rgb);
}

Check out my mix(), tint(), tone(), and shade() PHP functions: https://gist.github.com/andrewrcollins/4570993