chromium/chrome/test/data/banners/background-color.html

<html>
  <head>
    <title>Manifest test app with background color</title>
    <link rel="manifest" href="background-color.json">
    <meta id="background-color" name="background-color" content="blue">
    <script>
      window.onload = () => {
        navigator.serviceWorker.register('service_worker_empty_fetch_handler.js');
      };
    </script>
  </head>
  <body>
    Manifest test app with a background color.
  </body>
</html>