Flutter Container: cannot provide both a color and a decoration

Remove the color parameter from the Container and add it to the BoxDecoration:

Widget bodyWidget() {
  return Container(
    decoration: BoxDecoration(
      color: Colors.yellow,
      border: Border.all(color: Colors.black),
    ),
    child: Text("Flutter"),
  );
}

If you check the Container source code you can see that the color parameter is just used to set the BoxDecoration color if the decoration is null.

decoration = decoration ?? (color != null ? BoxDecoration(color: color) : null),

The error you got is just a helpful reminder of that. Otherwise you would get a strange override (as was apparently the case in the past) or you might not even notice the bug.