color_filter.dart

class _MyHomePageState extends State<MyHomePage> {
  final String myImageUrl =
      "https://images.unsplash.com/photo-1485841890310-6a055c88698a?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1350&q=80"; // <- defines the url path of our image

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Container(
        color: Colors.red,
        child: ColorFiltered(   // <- wrap yor image with a Color Filtered widget
          colorFilter: ColorFilter.mode(Colors.grey, BlendMode.saturation), <-  // Our grey filter
          child: Center(
            child: Image.network(myImageUrl),
          ),
        ),
      ),
    );
  }
}