你可以
在下面复制粘贴运行完整的代码，在这种情况下，你可以使用ValueNotifier<Color>和ValueListenableBuilder
代码段

ValueNotifier<Color> currentColor = ValueNotifier(Colors.grey);
...
MaterialPicker(
    pickerColor: currentColor.value,
...
child: const Text('Change me'),
              color: currentColor.value,
...
list.add(ValueListenableBuilder(
                        valueListenable: currentColor,
                        builder: (BuildContext context, Color current,
                            Widget child) {
                          return Positioned(
                            left: 100,
                            top: 100,
                            child: Container(
                              color: current,
                              height: 100,
                              width: 100,
                            ),
                          );
                        }));    

工作演示

完整的代码

import 'package:flutter/material.dart';
import 'package:flutter_colorpicker/flutter_colorpicker.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Test(),
    );
  }
}

class Test extends StatefulWidget {
  @override
  _TestState createState() => _TestState();
}

class _TestState extends State<Test> {
  ValueNotifier<Color> currentColor = ValueNotifier(Colors.grey);

  void changecolor(Color color) {
    setState(() {
      currentColor.value = color;
    });
  }

  List<Widget> list = [];

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Stack(
        children: [
          Container(
            height: MediaQuery.of(context).size.height,
            width: MediaQuery.of(context).size.width,
          ),
          Positioned(
            right: 50,
            top: 50,
            child: RaisedButton(
              elevation: 3.0,
              onPressed: () {
                showDialog(
                  context: context,
                  builder: (BuildContext context) {
                    return AlertDialog(
                      titlePadding: const EdgeInsets.all(0.0),
                      contentPadding: const EdgeInsets.all(0.0),
                      content: SingleChildScrollView(
                        child: MaterialPicker(
                          pickerColor: currentColor.value,
                          onColorChanged: changecolor,
                          enableLabel: true,
                        ),
                      ),
                    );
                  },
                );
              },
              child: const Text('Change me'),
              color: currentColor.value,
            ),
          ),
          ...list,
          Positioned(
            left: 50,
            top: 50,
            child: RaisedButton(
              child: Text(
                'Add another Color Sticker',
                style: TextStyle(fontSize: 10),
              ),
              onPressed: () {
                setState(
                  () {
                    list.add(ValueListenableBuilder(
                        valueListenable: currentColor,
                        builder: (BuildContext context, Color current,
                            Widget child) {
                          return Positioned(
                            left: 100,
                            top: 100,
                            child: Container(
                              color: current,
                              height: 100,
                              width: 100,
                            ),
                          );
                        }));
                  },
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}