function rgb2hex(rgb) {
  if (rgb.search("rgb") == -1) {
    return rgb;
  } else {
    rgb = rgb.match(/^rgba?\((\d+),\s*(\d+),\s*(\d+)(?:,\s*(\d+))?\)$/);
    function hex(x) {
      return ("0" + parseInt(x).toString(16)).slice(-2);
    }
    return "#" + hex(rgb[1]) + hex(rgb[2]) + hex(rgb[3]);
  }
}

var keys = Object.keys(window.getComputedStyle($0)).filter(r =>
  /color/gi.test(r)
);
[
  ...Array.from(document.querySelectorAll("*")).reduce((colors, el) => {
    keys.forEach(ee => {
      colors.add(getComputedStyle(el)[ee]);
    });
    return colors;
  }, new Set())
]
  .map(n => {
    try {
      return rgb2hex(n);
    } catch (e) {
      return null;
    }
  })
  .filter(ab => typeof ab === "string" && ab.indexOf("#") === 0)
  .toString();