popup.js

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

'use strict'

const changeColor = document.getElementById('changeColor')

chrome.storage.sync.get('color', function (data) {
  changeColor.style.backgroundColor = data.color
  changeColor.setAttribute('value', data.color)
})

changeColor.onclick = function (element) {
  const color = element.target.value
  chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) {
    chrome.tabs.executeScript(
      tabs[0].id,
      { code: 'document.body.style.backgroundColor = "' + color + '";' })
  })
};