protected function adjustHsl($color, $idx, $amount) { $hsl = $this->toHSL($color[1], $color[2], $color[3]); $hsl[$idx] += $amount; $out = $this->toRGB($hsl[1], $hsl[2], $hsl[3]); if (isset($color[4])) { $out[4] = $color[4]; } return $out; }