给定一个颜色值，如何把它转换成一个深一点的值

$a = "#333333";
$rgb = unpack('C*', pack('H*', substr($a, 1)));
$hsb = call_user_func_array('rgb2hsb', $rgb);
$hsb[2] *= 0.67;
$rgb = call_user_func_array('hsb2rgb', $hsb);
echo '#' . join('', array_map('dechex', $rgb));


function rgb2hsb($rgbR, $rgbG, $rgbB) {
    $rgbR &= 255;
    $rgbG &= 255;
    $rgbB &= 255;
    $rgb = array($rgbR, $rgbG, $rgbB );
    sort($rgb);
    $max = $rgb[2];
    $min = $rgb[0];
 
    $hsbB = $max / 255.0;
    $hsbS = $max == 0 ? 0 : ($max - $min) / $max;
 
    $hsbH = 0;
    if ($max == $rgbR && $rgbG >= $rgbB) {
        $hsbH = ($rgbG - $rgbB) * 60 / (($m = $max - $min) ? $m : 1);
    } else if ($max == $rgbR && $rgbG < $rgbB) {
        $hsbH = ($rgbG - $rgbB) * 60 / ($max - $min) + 360;
    } else if ($max == $rgbG) {
        $hsbH = ($rgbB - $rgbR) * 60 / ($max - $min) + 120;
    } else if ($max == $rgbB) {
        $hsbH = ($rgbR - $rgbG) * 60 / ($max - $min) + 240;
    }
 
    return array( $hsbH, $hsbS, $hsbB );
}
 
function hsb2rgb($h, $s, $v) {
    $r = $g = $b = 0;
    $i = ($h / 60) % 6;
    $f = ($h / 60) - $i;
    $p = $v * (1 - $s);
    $q = $v * (1 - $f * $s);
    $t = $v * (1 - (1 - $f) * $s);
    switch ($i) {
    case 0:
        $r = $v;
        $g = $t;
        $b = $p;
        break;
    case 1:
        $r = $q;
        $g = $v;
        $b = $p;
        break;
    case 2:
        $r = $p;
        $g = $v;
        $b = $t;
        break;
    case 3:
        $r = $p;
        $g = $q;
        $b = $v;
        break;
    case 4:
        $r = $t;
        $g = $p;
        $b = $v;
        break;
    case 5:
        $r = $v;
        $g = $p;
        $b = $q;
        break;
    default:
        break;
    }
    return array( intval($r * 255), intval($g * 255), intval($b * 255) );
}