const isColorDark = color => {
  const c = color.substring(1);      // strip #
  const rgb = parseInt(c, 16);   // convert rrggbb to decimal
  const r = (rgb >> 16) & 0xff;  // extract red
  const g = (rgb >>  8) & 0xff;  // extract green
  const b = (rgb >>  0) & 0xff;  // extract blue

  const luma = 0.2126 * r + 0.7152 * g + 0.0722 * b; // per ITU-R BT.709
  const isDark = luma < 40;

  return isDark;
}