color-list.js

Object.entries(Array.from(document.querySelectorAll('*'))
.reduce((list, el) => {
  const styles = window.getComputedStyle(el);
  Object.values(styles).forEach((prop) => {
    const value = styles[prop];
    if (prop.toLowerCase().includes('color')) {
      (value.match(/rgba?\(\d+, \d+, \d+(, \d+(.\d+)?\))?/g) || [])
        .map(s => (s.match(/\d+(.\d+)?/g) || []).join(', '))
        .forEach((color) => {
          if (!(color in list)) {
            list[color] = [];
          }
          if (!list[color].includes(el)) {
            list[color].push(el)
          }
        });
    }
  });
  return list;
}, {}))
.forEach(([sCodes, els]) => console.log(`%c ${sCodes} (${els.length}) `, `background-color: ${sCodes.length === 3 ? 'rgb' : 'rgba'}(${sCodes}); text-shadow: 1px 1px #fff`));

// EOF

This may take so long time that your browser gets stuck. 🐘