title: How to give a gradient line in tab bar indicator
body: <p>I have a tab bar functionality in which I show a Donut chart and list of vehicles but I need to show which tab the user selected for that I have indicatorColor in TabBar but I need to fill with gradient line as shown in the image please help me out.</p>
  
  <p>PS: If possible please let me know how to give theme color means primary color in main as a gradient???</p>
  
  <pre><code>return Scaffold(
      body: new DefaultTabController(
          length: 2,
          child: new Column(
            children: &lt;Widget&gt;[
              new Container(
                width: 1200.0,
                child: new Container(
                  color: Colors.white,
                  child: new TabBar(
                    labelColor: Colors.black,
                    tabs: [
                      Tab(
                        child: new Text("Visual",
                        style: new TextStyle(fontSize: 20.0)
                        ),
                      ),
  
                      Tab(
                        child: new Text("Tabular",
                        style: new TextStyle(fontSize: 20.0)), 
                      ),
                    ],
                  ),
                ),
              ),
              new Expanded(
                child: new TabBarView(
                  children: [
                    Tab(
                      child: new RefreshIndicator(
                        child: new Text('DONUT CHART'),
                        onRefresh: refreshList,
                        key: refreshKey1,
                      ),
                    ),
                    Tab(
                      child: new RefreshIndicator(
                        child: new Text('List of vehicles'),
                        onRefresh: refreshList,
                        key: refreshKey2,
                      ),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
      );
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/cy9cz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cy9cz.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/mxAZW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mxAZW.png" alt="enter image description here"></a></p>