Simple example to show the invisible divider.

divider.dart

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    title: 'divider',
    home: new ExpandedWidget(),
  ));
}

class ExpandedWidget extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('divider'),
      ),
      body: new Container(
        child: new Row(
          children: [
            new Column(
              children: [
                new Text('Hello'),
                new Divider(
                  indent: 10.0,
                  height: 50.0,
                  color: new Color.fromRGBO(255, 255, 255, 1.0)
                ),
                new Text('World'),
              ]
            ),
          ]
        ),
        color: new Color.fromRGBO(100, 100, 100, 1.0),
      )
    );
  }
}