Flutter app - get Material You colors via platform channel

main.dart

import 'package:flutter/material.dart';
import 'package:materialyou_demo/platform_colors.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: getMaterialYouColor(),
      builder: (context, AsyncSnapshot<MaterialYouPalette?> snapshot) {
        final primarySwatch = snapshot.data?.accent1 ?? Colors.blue;
        final accent2Swatch = snapshot.data?.accent2 ?? Colors.blue;
        final accent3Swatch = snapshot.data?.accent3 ?? Colors.blue;
        return MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: primarySwatch,
            checkboxTheme: CheckboxThemeData(
              fillColor: MaterialStateProperty.resolveWith((states) => accent2Swatch),
            ),
            elevatedButtonTheme: ElevatedButtonThemeData(
              style: ButtonStyle(
                backgroundColor: MaterialStateProperty.resolveWith((states) => accent3Swatch),
              ),
            ),
            floatingActionButtonTheme: FloatingActionButtonThemeData(
              backgroundColor: accent3Swatch.shade300,
            ),
            bottomNavigationBarTheme: BottomNavigationBarThemeData(
              backgroundColor: accent2Swatch.shade100,
              selectedIconTheme: IconThemeData(
                color: accent2Swatch.shade900,
              ),
              unselectedIconTheme: IconThemeData(
                color: accent2Swatch.shade300,
              ),
              selectedItemColor: Colors.black,
              unselectedItemColor: Colors.black,
            ),
          ),
          home: const _HomePage(),
        );
      },
    );
  }
}

class _HomePage extends StatelessWidget {
  const _HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Demo'),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.add),
            label: 'First',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.access_alarm),
            label: 'Two',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.ac_unit),
            label: 'Three',
          ),
        ],
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'Here are some widgets for you:',
            ),
            Switch(
              value: true,
              onChanged: (_) {},
            ),
            Checkbox(
              value: true,
              onChanged: (_) {},
            ),
            ElevatedButton(
              onPressed: () {},
              child: const Text('Material button'),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

MainActivity.kt

package com.example.materialyou_demo

import android.os.Build
import androidx.core.content.res.ResourcesCompat
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel

class MainActivity : FlutterActivity() {
    private val CHANNEL = "com.example.app/colors"

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)

        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
                call,
                result ->
            when (call.method) {
                "getMaterialYouColors" -> result.success(getMaterialYouColors())
                else -> result.notImplemented()
            }
        }
    }

    private fun getMaterialYouColors(): String? {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.S) {
            return null
        }

        return mapOf(
                        "system_accent1_0" to android.R.color.system_accent1_0,
                        "system_accent1_10" to android.R.color.system_accent1_10,
                        "system_accent1_50" to android.R.color.system_accent1_50,
                        "system_accent1_100" to android.R.color.system_accent1_100,
                        "system_accent1_200" to android.R.color.system_accent1_200,
                        "system_accent1_300" to android.R.color.system_accent1_300,
                        "system_accent1_400" to android.R.color.system_accent1_400,
                        "system_accent1_500" to android.R.color.system_accent1_500,
                        "system_accent1_600" to android.R.color.system_accent1_600,
                        "system_accent1_700" to android.R.color.system_accent1_700,
                        "system_accent1_800" to android.R.color.system_accent1_800,
                        "system_accent1_900" to android.R.color.system_accent1_900,
                        "system_accent1_1000" to android.R.color.system_accent1_1000,

                        "system_accent2_0" to android.R.color.system_accent2_0,
                        "system_accent2_10" to android.R.color.system_accent2_10,
                        "system_accent2_50" to android.R.color.system_accent2_50,
                        "system_accent2_100" to android.R.color.system_accent2_100,
                        "system_accent2_200" to android.R.color.system_accent2_200,
                        "system_accent2_300" to android.R.color.system_accent2_300,
                        "system_accent2_400" to android.R.color.system_accent2_400,
                        "system_accent2_500" to android.R.color.system_accent2_500,
                        "system_accent2_600" to android.R.color.system_accent2_600,
                        "system_accent2_700" to android.R.color.system_accent2_700,
                        "system_accent2_800" to android.R.color.system_accent2_800,
                        "system_accent2_900" to android.R.color.system_accent2_900,
                        "system_accent2_1000" to android.R.color.system_accent2_1000,

                        "system_accent3_0" to android.R.color.system_accent3_0,
                        "system_accent3_10" to android.R.color.system_accent3_10,
                        "system_accent3_50" to android.R.color.system_accent3_50,
                        "system_accent3_100" to android.R.color.system_accent3_100,
                        "system_accent3_200" to android.R.color.system_accent3_200,
                        "system_accent3_300" to android.R.color.system_accent3_300,
                        "system_accent3_400" to android.R.color.system_accent3_400,
                        "system_accent3_500" to android.R.color.system_accent3_500,
                        "system_accent3_600" to android.R.color.system_accent3_600,
                        "system_accent3_700" to android.R.color.system_accent3_700,
                        "system_accent3_800" to android.R.color.system_accent3_800,
                        "system_accent3_900" to android.R.color.system_accent3_900,
                        "system_accent3_1000" to android.R.color.system_accent3_1000,

                        "system_neutral1_0" to android.R.color.system_neutral1_0,
                        "system_neutral1_10" to android.R.color.system_neutral1_10,
                        "system_neutral1_50" to android.R.color.system_neutral1_50,
                        "system_neutral1_100" to android.R.color.system_neutral1_100,
                        "system_neutral1_200" to android.R.color.system_neutral1_200,
                        "system_neutral1_300" to android.R.color.system_neutral1_300,
                        "system_neutral1_400" to android.R.color.system_neutral1_400,
                        "system_neutral1_500" to android.R.color.system_neutral1_500,
                        "system_neutral1_600" to android.R.color.system_neutral1_600,
                        "system_neutral1_700" to android.R.color.system_neutral1_700,
                        "system_neutral1_800" to android.R.color.system_neutral1_800,
                        "system_neutral1_900" to android.R.color.system_neutral1_900,
                        "system_neutral1_1000" to android.R.color.system_neutral1_1000,

                        "system_neutral2_0" to android.R.color.system_neutral2_0,
                        "system_neutral2_10" to android.R.color.system_neutral2_10,
                        "system_neutral2_50" to android.R.color.system_neutral2_50,
                        "system_neutral2_100" to android.R.color.system_neutral2_100,
                        "system_neutral2_200" to android.R.color.system_neutral2_200,
                        "system_neutral2_300" to android.R.color.system_neutral2_300,
                        "system_neutral2_400" to android.R.color.system_neutral2_400,
                        "system_neutral2_500" to android.R.color.system_neutral2_500,
                        "system_neutral2_600" to android.R.color.system_neutral2_600,
                        "system_neutral2_700" to android.R.color.system_neutral2_700,
                        "system_neutral2_800" to android.R.color.system_neutral2_800,
                        "system_neutral2_900" to android.R.color.system_neutral2_900,
                        "system_neutral2_1000" to android.R.color.system_neutral2_1000
                )
                .map { (name, id) ->
                    val color = ResourcesCompat.getColor(resources, id, theme)
                    val colorHex = Integer.toHexString(color)
                    return@map "\"$name\": \"#$colorHex\""
                }
                .joinToString(separator = ",", prefix = "{", postfix = "}")
    }
}

platform_colors.dart

import 'dart:convert';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

const platform = MethodChannel('com.example.app/colors');

Future<MaterialYouPalette?> getMaterialYouColor() async {
  // Material You colors are available on Android only
  if (defaultTargetPlatform != TargetPlatform.android) return null;

  try {
    final data = await platform.invokeMethod('getMaterialYouColors');
    if (data == null) return null;

    final Map<String, dynamic> items = (json.decode(data) as Map<String, dynamic>);
    return MaterialYouPalette(
      accent1: items.getAccent1(),
      accent2: items.getAccent2(),
      accent3: items.getAccent3(),
      neutral1: items.getNeutral1(),
      neutral2: items.getNeutral2(),
    );
  } on PlatformException catch (_) {
    return null;
  }
}

class MaterialYouPalette {
  final MaterialColor accent1;
  final MaterialColor accent2;
  final MaterialColor accent3;
  final MaterialColor neutral1;
  final MaterialColor neutral2;

  MaterialYouPalette({
    required this.accent1,
    required this.accent2,
    required this.accent3,
    required this.neutral1,
    required this.neutral2,
  });
}

int _parseHexString(String value) => int.parse(value.substring(3, 9), radix: 16) + 0xFF000000;

extension _ColorExtractionExtension on Map<String, dynamic> {
  Color getColor(String colorName) {
    final value = this[colorName];
    final parsed = _parseHexString(value);
    return Color(parsed);
  }

  MaterialColor getAccent1() {
    return MaterialColor(
      _parseHexString(this['system_accent1_100']),
      <int, Color>{
        50: getColor('system_accent1_50'),
        100: getColor('system_accent1_100'),
        200: getColor('system_accent1_200'),
        300: getColor('system_accent1_300'),
        400: getColor('system_accent1_400'),
        500: getColor('system_accent1_500'),
        600: getColor('system_accent1_600'),
        700: getColor('system_accent1_700'),
        800: getColor('system_accent1_800'),
        900: getColor('system_accent1_900'),
      },
    );
  }

  MaterialColor getAccent2() {
    return MaterialColor(
      _parseHexString(this['system_accent2_100']),
      <int, Color>{
        50: getColor('system_accent2_50'),
        100: getColor('system_accent2_100'),
        200: getColor('system_accent2_200'),
        300: getColor('system_accent2_300'),
        400: getColor('system_accent2_400'),
        500: getColor('system_accent2_500'),
        600: getColor('system_accent2_600'),
        700: getColor('system_accent2_700'),
        800: getColor('system_accent2_800'),
        900: getColor('system_accent2_900'),
      },
    );
  }

  MaterialColor getAccent3() {
    return MaterialColor(
      _parseHexString(this['system_accent3_100']),
      <int, Color>{
        50: getColor('system_accent3_50'),
        100: getColor('system_accent3_100'),
        200: getColor('system_accent3_200'),
        300: getColor('system_accent3_300'),
        400: getColor('system_accent3_400'),
        500: getColor('system_accent3_500'),
        600: getColor('system_accent3_600'),
        700: getColor('system_accent3_700'),
        800: getColor('system_accent3_800'),
        900: getColor('system_accent3_900'),
      },
    );
  }

  MaterialColor getNeutral1() {
    return MaterialColor(
      _parseHexString(this['system_neutral1_100']),
      <int, Color>{
        50: getColor('system_neutral1_50'),
        100: getColor('system_neutral1_100'),
        200: getColor('system_neutral1_200'),
        300: getColor('system_neutral1_300'),
        400: getColor('system_neutral1_400'),
        500: getColor('system_neutral1_500'),
        600: getColor('system_neutral1_600'),
        700: getColor('system_neutral1_700'),
        800: getColor('system_neutral1_800'),
        900: getColor('system_neutral1_900'),
      },
    );
  }

  MaterialColor getNeutral2() {
    return MaterialColor(
      _parseHexString(this['system_neutral2_100']),
      <int, Color>{
        50: getColor('system_neutral2_50'),
        100: getColor('system_neutral2_100'),
        200: getColor('system_neutral2_200'),
        300: getColor('system_neutral2_300'),
        400: getColor('system_neutral2_400'),
        500: getColor('system_neutral2_500'),
        600: getColor('system_neutral2_600'),
        700: getColor('system_neutral2_700'),
        800: getColor('system_neutral2_800'),
        900: getColor('system_neutral2_900'),
      },
    );
  }
}

For anyone interested, I've put this code in a library on github: https://github.com/Mause/material_you_colours

Cool! The link doesn't seem to work though

@aednlaxer oops sorry, set to public now