https://github.com/flutter/flutter/issues/47643

indicator_assert.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {
  TabController controller;
  List<Tab> tabs = [ Tab(text: 'Tab 1'), Tab(text: 'Tab 2') ];

  @override
  void initState() {
    controller = TabController(vsync: this, length: 2);
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        elevation: 0.1,
        backgroundColor:Color(0xffffffff),
        title: TabBar(
          controller: controller,
          tabs: tabs,
          indicator: UnderlineTabIndicator(
            borderSide: BorderSide(width: 0.0, color: Colors.white),
            insets: EdgeInsets.zero,
          ),
          indicatorWeight: 0.01,
          indicatorSize: TabBarIndicatorSize.tab,
        ),
        bottom: TabBar(
          controller: controller,
          labelColor: Colors.blue,
          tabs: <Widget>[
            Text('Tab 1'),
            Text('Tab 2'),
          ],
        ),
      ),
      body: Center(child: Text('Hello World'),),
    );
  }
}