code: function RGBA_TO_CMYK() {
          var r = this.r() / 255;
          var g = this.g() / 255;
          var b = this.b() / 255;
          var black = 1 - Math.max(r, g, b);
  
          if (black === 0) {
              return kolor.cmyk(0, 0, 0, 0);
          }
  
          var c = (1 - r - black) / (1 - black);
          var m = (1 - g - black) / (1 - black);
          var y = (1 - b - black) / (1 - black);
          return kolor.cmyk(c, m, y, black, this.a());
      }
docs: Naively converts RGBA color to CMYK