Scrollable Container inside a Column

I think that maybe after a year you have managed to do that.

But for others searching for the same problem, the easiest way is to wrap the SingleChildScrollView inside an Expanded widget.

Widget build(BuildContext context) =>
Scaffold(
  body: Column(
    children: <Widget>[
      Container(
        height: 100.0,
        color: Colors.blue,
      ),
      Expanded(
        child: SingleChildScrollView(
          child: Container(
            color: Colors.red,
            padding: EdgeInsets.all(20.0),
            child: Column(
              children: <Widget>[
                Text('Red container should be scrollable'),
                Container(
                  width: double.infinity,
                  height: 700.0,
                  padding: EdgeInsets.all(10.0),
                  color: Colors.white.withOpacity(0.7),
                  child: Text('I will have a column here'),
                )
              ],
            ),
          ),
        ),
      ),
    ],
  ),
);