title: React Navigation set individual tab colors
body: <p>Can't seem to figure out how to change the "activeTintColor" for individual tabs on my TabNavigator</p>
  
  <p>basic setup is here, where and what do I insert to set the activeTintColor for each tab instead of all 3</p>
  
  <pre><code>const MainApp = TabNavigator({
    Tab1: { screen: Screen1, 
      navigationOptions: { title: 'Screen 1'}
    },
    Tab2: { screen: Screen2, 
      navigationOptions: { title: 'Screen 2'}
    },
    Tab3: { screen: Screen3, 
      navigationOptions: { title: 'Screen 3'}
    }
  },{
    tabBarPosition: 'bottom',
    tabBarOptions: {
      //activeTintColor: "this sets it for all 3"
    },
  });
  </code></pre>