定义
        HSL即色相、饱和度、亮度（英语：Hue, Saturation, Lightness）。
        色相（H）是色彩的基本属性，就是平常所说的颜色名称，如红色、黄色等。可以说和光谱对应。取值为0-360度。
        饱和度（S）是指色彩的纯度，越高色彩越纯，低则逐渐变灰，取0-100%的数值。
        明度（V），亮度（L），取0-100%。
        如图所示，圆柱从低向上，表示亮度，由中轴向外表示饱和度，水平截面的圆周角表示色相。

        如果用圆锥表示则为双圆锥：这种表示放法相比较圆柱更加直观，最低端的只用一个点表示黑色，如果用圆柱，用了一面表示黑色，无太大意义。从圆锥上可以看出，亮度的调节会影响颜色的丰富程度。

        这种表示相比RGB更加直观，比如：白色可以直接将亮度设置为100%,而RGB需要设置三个通道。比如颜色想从黄色过度到红色，只需要调整色相即可，饱和度和亮度保持不变，而RGB调节相对就比较复杂且不直观。HSL一般更适用于用户，而RGB更适用于显示领域。

常用颜色

        

转换
HSL和RGB的相互转换百度百科有详细介绍。此处截图说明转换公式：

void RGB2HSL(in float3 rgb, out float3 hsl)
{
    float precision = 0.00001f;
    float rgbMax = max(max(rgb.r, rgb.g), rgb.b);
    float rgbMin = min(min(rgb.r, rgb.g), rgb.b);

    //hue
    [flatten]
    if (abs(rgbMax - rgbMin) < precision) // max == min
    {
        hsl.r = 0.0f;
    }
    else if (abs(rgbMax - rgb.r) < precision) // max == r
    {
        hsl.r = 60.0f * (rgb.g - rgb.b) / (rgbMax - rgbMin);
        if (rgb.g < rgb.b)
            hsl.r += 360.0f;
    }
    else if (abs(rgbMax - rgb.g) < precision) // max == g
    {
        hsl.r = 60.0f * (rgb.b - rgb.r) / (rgbMax - rgbMin) + 120.0f;
    }
    else if (abs(rgbMax - rgb.g) < precision) // max == b
    {
        hsl.r = 60.0f * (rgb.r - rgb.g) / (rgbMax - rgbMin) + 240.0f;
    }
      // light
    hsl.b = (rgbMax + rgbMin) / 2.0f;
     // saturation
    [flatten]
    if (hsl.b <= precision || abs(rgbMax - rgbMin) < precision)
    {
        hsl.g = 0.0f;
    }
    else if (hsl.b > 0.0f && hsl.b <= 0.5f)
    {
        hsl.g = (rgbMax - rgbMin) / (rgbMax + rgbMin);
    }
     else if (hsl.b > 0.5f)
    {
        hsl.g = (rgbMax - rgbMin) / (2 - (rgbMax + rgbMin));
    }
  }

float ToColor(float p, float q, float t)
{
    [flatten]
    if (t < 0.0f)
        t = t + 1.0f;
    else if (t > 1.0f)
        t = t - 1.0f;
    float c = 0.0f;
    [flatten]
    if (t < 0.166667f)
    {
        c = p + ((q - p) * 6 * t);
    }
    else if (t >= 0.166667f && t < 0.5f)
    {
        c = q;
    }
     else if (t >= 0.5f && t < 0.66667f)
    {
        c = p + ((q - p) * 6 * (0.66667f - t));
    }
    else
    {
        c = p;
    }
    return c;
}

void HSL2RGB(in float3 hsl, out float3 rgb)
{
    float precision = 0.00001f;
    [flatten]
    float hue = hsl.r;
    float sat = hsl.g;
    float light = hsl.b;
     if (sat < precision) // sat == 0
    {
        rgb = hsl.bbb;
    }
     else
    {
        float q = 0.0f, p = 0.0f, hk = 0.0;
        if (light < 0.5f)
        {
            q = light * (1 + sat);
        }
         else
        {
            q = light + sat - (light * sat);
        }
          p = 2.0f * light - q;
        hk = hue / 360.0f;
        rgb.r = ToColor(p, q, hk + 0.33333f);
        rgb.g = ToColor(p, q, hk);
        rgb.b = ToColor(p, q, hk - 0.33333f);
    }
}

php版本

colors - PHP HSV to RGB formula comprehension - Stack Overflow

<?php    
    $hue = 209;
    $sat = 75;
    $lum = 60;

    $hue /= 360;
    $sat /= 100;
    $lum /= 100;

    $result = ColorHSLToRGB($hue, $sat, $lum);
    var_dump($result); echo '<br>';
    printf("rgb = %d,%d,%d<br>", $result['r'], $result['g'], $result['b']);




function ColorHSLToRGB($h, $s, $l){

        $r = $l;
        $g = $l;
        $b = $l;
        $v = ($l <= 0.5) ? ($l * (1.0 + $s)) : ($l + $s - $l * $s);
        if ($v > 0){
              $m;
              $sv;
              $sextant;
              $fract;
              $vsf;
              $mid1;
              $mid2;

              $m = $l + $l - $v;
              $sv = ($v - $m ) / $v;
              $h *= 6.0;
              $sextant = floor($h);
              $fract = $h - $sextant;
              $vsf = $v * $sv * $fract;
              $mid1 = $m + $vsf;
              $mid2 = $v - $vsf;

              switch ($sextant)
              {
                    case 0:
                          $r = $v;
                          $g = $mid1;
                          $b = $m;
                          break;
                    case 1:
                          $r = $mid2;
                          $g = $v;
                          $b = $m;
                          break;
                    case 2:
                          $r = $m;
                          $g = $v;
                          $b = $mid1;
                          break;
                    case 3:
                          $r = $m;
                          $g = $mid2;
                          $b = $v;
                          break;
                    case 4:
                          $r = $mid1;
                          $g = $m;
                          $b = $v;
                          break;
                    case 5:
                          $r = $v;
                          $g = $m;
                          $b = $mid2;
                          break;
              }
        }
        return array('r' => $r * 255.0, 'g' => $g * 255.0, 'b' => $b * 255.0);
}
?>

js版本

/**
 * convert a HSL colorscheme to either Hexadecimal (default) or RGB.
 * 
 * We want a method where we can programmatically generate a series of colors
 * between two values (eg. red to green) which is easy to do with HSL because
 * you just change the hue. (0 = red, 120 = green).  You can use this function
 * to convert those hsl color values to either the rgb or hexadecimal color scheme.
 * e.g. You have
 *   hsl(50, 100%, 50%)
 * To convert,
 * $hex = convertHSL(50,100,50);  // returns #ffd500
 * or 
 * $rgb = convertHSL(50,100,50, false);  // returns rgb(255, 213, 0)
 *  
 * see https://coderwall.com/p/dvsxwg/smoothly-transition-from-green-to-red
 * @param int $h the hue
 * @param int $s the saturation
 * @param int $l the luminance
 * @param bool $toHex whether you want hexadecimal equivalent or rgb equivalent
 * @return string usable in HTML or CSS
 */

function convertHSL($h, $s, $l, $toHex=true){
    $h /= 360;
    $s /=100;
    $l /=100;

    $r = $l;
    $g = $l;
    $b = $l;
    $v = ($l <= 0.5) ? ($l * (1.0 + $s)) : ($l + $s - $l * $s);
    if ($v > 0){
          $m;
          $sv;
          $sextant;
          $fract;
          $vsf;
          $mid1;
          $mid2;

          $m = $l + $l - $v;
          $sv = ($v - $m ) / $v;
          $h *= 6.0;
          $sextant = floor($h);
          $fract = $h - $sextant;
          $vsf = $v * $sv * $fract;
          $mid1 = $m + $vsf;
          $mid2 = $v - $vsf;

          switch ($sextant)
          {
                case 0:
                      $r = $v;
                      $g = $mid1;
                      $b = $m;
                      break;
                case 1:
                      $r = $mid2;
                      $g = $v;
                      $b = $m;
                      break;
                case 2:
                      $r = $m;
                      $g = $v;
                      $b = $mid1;
                      break;
                case 3:
                      $r = $m;
                      $g = $mid2;
                      $b = $v;
                      break;
                case 4:
                      $r = $mid1;
                      $g = $m;
                      $b = $v;
                      break;
                case 5:
                      $r = $v;
                      $g = $m;
                      $b = $mid2;
                      break;
          }
    }
    $r = round($r * 255, 0);
    $g = round($g * 255, 0);
    $b = round($b * 255, 0);

    if ($toHex) {
        $r = ($r < 15)? '0' . dechex($r) : dechex($r);
        $g = ($g < 15)? '0' . dechex($g) : dechex($g);
        $b = ($b < 15)? '0' . dechex($b) : dechex($b);
        return "#$r$g$b";
    } else {
        return "rgb($r, $g, $b)";    
    }

参考

RGB 和 HSL 的转换和应用-CSDN博客

RGB 与HSL 色彩空间的转换函数-Excel VBA程序开发-ExcelHome技术论坛 -

HSL（色彩模式）_百度百科

显示屏色域、色深、色差等参数 - 知乎

在线转换工具

RGB到HSL颜色转换 - RGB到色相、饱和度、亮度转换

HSL到RGB颜色转换