How to change radio's inactive color in Flutter?

Radio uses unselectedWidgetColor of ThemeData. If you need to change it only for a few radios on a specific screen, wrap them in Theme widget to override a color:

Theme(  data: Theme.of(context).copyWith(    unselectedWidgetColor: Colors.red,    disabledColor: Colors.blue  ),  child: Column(    children: <Widget>[      ListTile(        onTap: () => setState(() => value = 0),        leading: Radio(          value: 0,          groupValue: value,          onChanged: (v) => setState(() => value = v),        )      ),      ListTile(        onTap: () => setState(() => value = 1),        leading: Radio(          value: 1,          groupValue: value,          onChanged: (v) => setState(() => value = v),        )      ),    ],  ),)

If no callback passed in onChanged to Radio, it is interpreted as disabled (this works for many default material widgets).

You can also set the fillColor propery, it resolves a color for multiple radio states. In this case, it returns Colors.blue for all states.

Radio(          fillColor: MaterialStateColor.resolveWith((states) => Colors.blue),          value: 1,          groupValue: _optionValue,          onChanged: changeValue,        )