给定一个颜色值，怎么把它转换成一个深一点的值？

a = "#333333"
需要这个函数：把a的色彩变深一点，比如a="#222222"

回复讨论(解决方案)

$a = "#333333";$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) );}

感谢！