workaround show hint and selectedItemBuilder together

dropdownformcolor.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

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

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  void _incrementCounter() {
    setState(() {});
  }

  List<String> options = <String>['One', 'Two', 'Free', 'Four'];
  String? dropdownValue;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            DropdownButton<String>(
              value: dropdownValue,
              style: const TextStyle(color: Colors.grey, fontSize: 15),
              hint: dropdownValue != null
                  ? null
                  : const Text(
                      'Select Value',
                      style: TextStyle(color: Colors.black),
                    ),
              onChanged: (value) => setState(() => dropdownValue = value),
              selectedItemBuilder: dropdownValue == null
                  ? null
                  : (BuildContext context) {
                      return ['ONE', 'TWO.', 'THREE'].map((String value) {
                        return Text(
                          dropdownValue!,
                          style: const TextStyle(color: Colors.green),
                        );
                      }).toList();
                    },
              items: ['ONE', 'TWO.', 'THREE']
                  .map<DropdownMenuItem<String>>((String value) {
                return DropdownMenuItem<String>(
                  value: value,
                  child: Text(value,
                      style:
                          const TextStyle(inherit: false, color: Colors.red)),
                );
              }).toList(),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}