Get dominant color from images in RGB or HEX

colorthief.js

// https://github.com/lokesh/color-thief
const ColorThief = require('colorthief');

// Preferences
const directory = './images';
const extension = 'jpg';
const filenames = [
  'loon-yyy-riven',
  'dining-agreed-gumball',
  'cowan-logs-bagged',
];

// Utility
const rgbToHex = (r, g, b) => {
  const values = [r, g, b].map((value) => {
    const hex = value.toString(16);
    return hex.length === 1 ? `0${hex}` : hex;
  });
  return `#${values.join('')}`;
};

// Conversion

const promises = [];

filenames.forEach((filename) => {
  const promise = ColorThief
    // When run in Node, this argument expects a path to the image.
    // https://lokeshdhakar.com/projects/color-thief/#api
    .getColor(`${directory}/${filename}.${extension}`)
    // Returns RGB value in [Number, Number, Number] form
    // https://lokeshdhakar.com/projects/color-thief/#api
    .then(([r, g, b]) => (rgbToHex(r, g, b)));
  promises.push(promise);
});

Promise.all(promises)
  .then((values) => { console.log(values); });