如何在颤动中更改TextFormField提示标签背景颜色

dependencies:
  flutter_form_builder: ^4.0.0

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

final ThemeData customTheme = ThemeData(
  primarySwatch: Colors.blue,
  inputDecorationTheme: InputDecorationTheme(
    filled: true,
    fillColor: Colors.grey[200], // 设置背景颜色
    focusedBorder: OutlineInputBorder(
      borderSide: BorderSide(color: Colors.blue),
    ),
    enabledBorder: OutlineInputBorder(
      borderSide: BorderSide(color: Colors.grey),
    ),
    labelStyle: TextStyle(color: Colors.grey),
  ),
);

FormBuilder(
  child: TextFormField(
    decoration: InputDecoration(
      labelText: '请输入内容',
    ),
  ),
  theme: customTheme,
)