chromium/chrome/test/data/web_apps/basic_with_theme_color.html

<!DOCTYPE html>
<html>
<head>
  <link rel="manifest" href="basic.json">
  <meta id="themeColor" name="theme-color" content="yellow" />
  <link rel="icon" href="basic-48.png">
</head>
<body>
  <h1>Basic web app</h1>
  <script>
    navigator.serviceWorker.register('/web_apps/service_worker.js');
  </script>
</body>
</html>