code: function rgb2hsl() {
      const
          R = this.R,
          G = this.G,
          B = this.B,
          min = Math.min( R, G, B ),
          max = Math.max( R, G, B ),
          delta = max - min;
  
      this.L = 0.5 * ( max + min );
  
      if ( delta < 0.000001 ) {
          this.H = 0;
          this.S = 0;
      } else {
          this.S = delta / ( 1 - Math.abs( ( 2 * this.L ) - 1 ) );
          if ( max === R ) {
              if ( G >= B ) {
                  this.H = INV6 * ( ( G - B ) / delta );
              } else {
                  this.H = 1 - ( INV6 * ( ( B - G ) / delta ) );
              }
          } else if ( max === G ) {
              this.H = INV6 * ( 2 + ( ( B - R ) / delta ) );
          } else {
              this.H = INV6 * ( 4 + ( ( R - G ) / delta ) );
          }
      }
  }
docs: Read R,G,B and write H,S,L.
  @this Color
  @returns {undefined}