Flutter Example that builds a MaterialDesign 3 colorScheme from an image

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  ColorScheme? _colorScheme;

  @override
  void initState() {
    super.initState();
    _loadColorScheme();
  }

  Future<void> _loadColorScheme() async {
    final imageProvider = await NetworkImage("https://picsum.photos/id/28/400/300");
    final colorScheme = await ColorScheme.fromImageProvider(
      provider: imageProvider,
      brightness: Brightness.dark,
    );

    if (mounted) {
      print('colorScheme set');
      setState(() {
        _colorScheme = colorScheme;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        colorScheme: _colorScheme ?? ColorScheme.dark(),
        brightness: Brightness.dark,
      ),
      home: Scaffold(
        backgroundColor: Theme.of(context).colorScheme.secondary,
        appBar: AppBar(title: Text("Dynamic Color Scheme")),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text(Theme.of(context).colorScheme.primary.toString()),
              Text(Theme.of(context).colorScheme.secondary.toString()),
              Text(Theme.of(context).colorScheme.tertiary.toString()),
              Text(Theme.of(context).colorScheme.surface.toString()),
            ],
          ),
        ),
      ),
    );
  }
}