Flutter how to set container background as transparent color

You can achieve this simply with this:

...
   color: Colors.red.withOpacity(0),
                            ...

you can specify how much opacity you want by using decimal value from 0 to 1, 0 being fully transparent while 1 being fully opaque .

You can also do as below

backgroundColor: Color.fromRGBO(r, g, b, 0)

The AlertDialog Widget has a backgroundColor property , just set it to transparent.

  AlertDialog(
              contentPadding: EdgeInsets.zero,
              backgroundColor: Colors.transparent,

And remove the BoxDecoration

Update Looks like backgroundColor is not available on Flutter 1.0.0 yet. (I'm on dev channel)

stable: https://github.com/flutter/flutter/blob/stable/packages/flutter/lib/src/material/dialog.dart

dev: https://github.com/flutter/flutter/blob/dev/packages/flutter/lib/src/material/dialog.dart

Checking the source code of Dialog , I found it was using the dialogBackgroundColor from theme. Try this easy way:

  showDialog(
          context: context,
          builder: (BuildContext context) {
            return Theme(
              data: Theme.of(context).copyWith(dialogBackgroundColor: Colors.transparent),
              child: AlertDialog(
                contentPadding: EdgeInsets.zero,
                content: Stack(
                  children: <Widget>[
                    Container(
                      margin: EdgeInsets.all(8.0),
                      color: Colors.white,
                      ...