In a ListTile of ExpansionPanelList, the trialing is already given as an arrow down, and when the ListTile is expanded, the arrow changes to arrow up.

However, it's dark in color. I added trailing: Icon(blah blah). This merely added an icon between the title and the default trailing button(arrow down).

How do I change the color of the default trailing button while keeping its versatility that it turns into an arrow up when the box is expanded?

I tried wrapping the ListTile in a theme, which was what someone recommended, but the color of the arrow down doesn't change as seen below:

```
Widget _buildPanel() {
    return ExpansionPanelList.radio(
      initialOpenPanelValue: 0,
      children: _data.map<ExpansionPanelRadio>((Item item) {
        return ExpansionPanelRadio(
          backgroundColor: Colors.black,
          canTapOnHeader: true,
          value: item.id,
          headerBuilder: (BuildContext context, bool isExpanded) {
            return Theme(
              data: Theme.of(context)
                  .copyWith(unselectedWidgetColor: Colors.white),
              child: ListTile(
                title: Text(item.headerValue,

...

```

Updated errors:
[![Error](https://i.stack.imgur.com/oy3f2.png)](https://i.stack.imgur.com/oy3f2.png)
[![Error continued](https://i.stack.imgur.com/8nkz0.png)](https://i.stack.imgur.com/8nkz0.png)