how do you invert a color in flutter?

Question

i have a widget that is used to create a gradient effect:

class GradientContainer extends StatelessWidget {
  final child;

  GradientContainer({@required this.child});
  @override
  Widget build(BuildContext context) {
    return Stack(children: [
      Positioned(
          left: 5,
          top: 17,
          bottom: 5,
          right: 9,
          child: ClipRRect(
            borderRadius: BorderRadius.circular(4),
            child: Container(
              decoration: BoxDecoration(
                  gradient: LinearGradient(
                      begin: Alignment.topLeft,
                      end: Alignment.bottomRight,
                      stops: [
                    0.0,
                    1.0
                  ],
                      colors: [
                    Colors.black.withOpacity(0.0),
                    Theme.of(context).scaffoldBackgroundColor.withOpacity(0.8),
                  ])),
            ),
          )),
      child,
    ]);
  }
}

this works great intill the user switches to dark theme and cannot sea the gradient very clearly. So, I would like to do something like Theme.of(context).scaffoldBackgroundColor.invertColor().withOpacity(0.8) so that I can get the inverted color of the body which allows me to create a good contrast on the gradient no matter the theme. Anyone know how to do this? I have tried looking online but all I could find is how to apply an invert filter onto an image.

Solution

As per http://www.vb-helper.com/howto_invert_color.html:

You can invert a color by subtracting each of its red, green, and blue components from 255. In other words:

new_red   = 255 - old_red
new_green = 255 - old_green
new_blue  = 255 - old_blue

Color invert(Color color) {
  final r = 255 - color.red;
  final g = 255 - color.green;
  final b = 255 - color.blue;

  return Color.fromARGB((color.opacity * 255).round(), r, g, b);
}

void main() {
  final inverted = invert(Colors.deepOrange);
}