title: Change checked mark color of checkbox in flutter
body: <p>I need to change check mark color of the checkbox in the flutter and there is no parameter is given to change color in Checkbox.</p>
  
  <pre><code>Checkbox(
     value: isCheck,
     activeColor: Colors.grey,
     onChanged: (bool value) {
     setState(() { isCheck = value;});
         })
  </code></pre>
  
  <p>dart class code</p>
  
  <pre><code>  const Checkbox({
      Key key,
      @required this.value,
      this.tristate = false,
      @required this.onChanged,
      this.activeColor,
      this.materialTapTargetSize,
    }) : assert(tristate != null),
         assert(tristate || value != null),
         super(key: key);
  </code></pre>