title: A value of type 'Color' can't be assigned to a variable of type 'String'
body: <p>i got an error while using Colors.black property from the material.dart library.</p>
  <p><strong>Error</strong> : A value of type 'Color' can't be assigned to a variable of type 'String'. Try changing the type of the variable, or casting the right-hand type to 'String'.</p>
  <pre><code>import 'package:flutter/material.dart';
  
  class Category {
    final String id;
    final String title;
    final String color;
  
    const Category({
      @required this.id, 
      @required this.title, 
      this.color = Colors.black,
      });
  }
  </code></pre>
  <p><a href="https://i.stack.imgur.com/EGsqj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EGsqj.png" alt="enter image description here" /></a></p>
  <p>any help will be appreciated</p>