Approach to get the right color values from the GW2 colors API like Cliff Spradlin explained here: https://forum-en.guildwars2.com/forum/community/api/API-Suggestion-Colors/2141987

gw2colors.php

<?php

// functions rgb2hsl and hsl2rgb required
// https://gist.github.com/codemasher/741f30e68c6e9c7921c7

// see it live over here: https://chillerlan.net/gw2color.php

// example values for "Hot Pink" on cloth, id 126
$b = 14; 	//brightness
$c = 1.21094; 	//contrast
$h = 340; 	//hue
$s = 0.820313; 	//saturation
$l = 1.44531; 	//lightness

// base color
$rgb = array(128, 26, 26);

// apply brightness and contrast
foreach($rgb as $k => $v){
	$rgb[$k] = (($v+$b)-128) * $c+128;
}

// convert to HSL
$hsl = rgb2hsl($rgb);

// apply shifts
$hsl[0] = ($hsl[0]*360+$h)/360;
$hsl[1] = $hsl[1]*$s;
$hsl[2] = $hsl[2]*$l;

// convert back to RGB
$rgb = hsl2rgb($hsl);

// round RGB values
foreach($rgb as $k => $v){
	$rgb[$k] = round($v);
	// "correct" values to be in range 0-255 according to
	// https://forum-en.guildwars2.com/forum/community/api/How-To-Colors-API/2146224
	if($rgb[$k]<0){$rgb[$k] = 0;}
	if($rgb[$k]>255){$rgb[$k] = 255;}
}

// final RGB value
print_r($rgb);

?>