# App.js

...
class GreenScreen extends Component {
  render() {
    return(
      <View style={styles.green}>
        ...
        <TouchableHighlight
          style={styles.button}
          onPress={() => this.props.navigation.navigate('Red')}
        >
          <Text style={styles.text}>Go to Red</Text>
        </TouchableHighlight>
      </View>
    );
  }
}

class RedScreen extends Component {
  render() {
    return(
      <View style={styles.red}>
      ...
        <TouchableHighlight
          style={styles.button}
          onPress={() => this.props.navigation.navigate('Landing')}
        >
          <Text style={styles.text}>Back to Green</Text>
        </TouchableHighlight>
        ...
      </View>
    );
  }
}
...