title: Flutter - InputDecoration border only when focused
body: <p>I am trying to Design a custom <code>TextFormField</code> and everything is working fine except that I only need to show a border when the <code>TextFormField</code> is focused (someone has tapped into it).</p>
  
  <p>As I don't think that is possible I tried to change the color of the border, but it seems to me that this color can only be set through the <code>hintColor</code> of the theme. But as the <code>hintColor</code> also changes the color of the hint Text being displayed i can't use that.</p>
  
  <pre><code>final theme = Theme.of(context);
  
  return new Theme(
    data: theme.copyWith(primaryColor: Colors.blue),
    child: TextFormField(
      autocorrect: false,
      style: TextStyle(color: Colors.green),
      decoration: new InputDecoration(
        fillColor: Colors.white,
        filled: true,
        contentPadding:
            EdgeInsets.only(bottom: 10.0, left: 10.0, right: 10.0),
        labelText: title,
      ),
      validator: this.validator,
      onSaved: (String newValue) {
        setMethod(newValue);
      },
    ),
  );
  </code></pre>
  
  <p>Does anyone have an idea how to solve this problem?</p>