StackNavigator:无法更改页眉标题的字体颜色

import React from 'react';
import { Text } from 'react-native';

const HeaderTitle = () => {
  return (
    <Text style={{ color: 'red' }}>My App</Text>
  );
};

export default HeaderTitle;

import { createStackNavigator } from 'react-navigation';
import HeaderTitle from './HeaderTitle';

const AppNavigator = createStackNavigator(
  {
    Home: {
      screen: HomeScreen,
      navigationOptions: {
        headerTitle: <HeaderTitle />,
      },
    },
    // other screens
  },
  {
    initialRouteName: 'Home',
  }
);

export default AppNavigator;