function hex2rgb($hex) {
$color = str_replace("#","",$hex);
$rgb = array("r" => hexdec(substr($color,0,2)),
"g" => hexdec(substr($color,2,2)),
"b" => hexdec(substr($color,4,2)));
return $rgb;
} // www.yx10011.com

function rgb2cmyk($var1,$g=0,$b=0) {
if (is_array($var1)) {
$r = $var1["r"];
$g = $var1["g"];
$b = $var1["b"];
} else {
$r=$var1;
}
$cyan = 255 - $r;
$magenta = 255 - $g;
$yellow = 255 - $b;
$black = min($cyan, $magenta, $yellow);
$cyan = @(($cyan - $black) / (255 - $black)) * 255;
$magenta = @(($magenta - $black) / (255 - $black)) * 255;
$yellow = @(($yellow - $black) / (255 - $black)) * 255;
return array("c" => $cyan / 255,
"m" => $magenta / 255,
"y" => $yellow / 255,
"k" => $black / 255);
}

$color=rgb2cmyk(hex2rgb("#FF0000"));