InkWell ripple over top of image in GridTile in Flutter

I was able to get a ripple to appear over the image by using a Stack and wrapping the InkWell in a Material widget.

return new Stack(children: <Widget>[
        new Positioned.fill(
          bottom: 0.0,
          child: new GridTile(
              footer: new GridTileBar(
                title: new Text(s.displayName),
                subtitle: new Text(s.gameName),
                backgroundColor: Colors.black45,
                trailing: new Icon(
                  Icons.launch,
                  color: Colors.white,
                ),
              ),
              child: new Image.network(s.imageSrc, fit: BoxFit.cover)),
        ),
        new Positioned.fill(
            child: new Material(
                color: Colors.transparent,
                child: new InkWell(
                  splashColor: Colors.lightGreenAccent,
                  onTap: () => _launchStream(s.displayName),
                ))),
      ]);