How to change checkbox border-color in flutter? By default, it is showing black but I want it in grey

Use this:

Checkbox(
  shape: RoundedRectangleBorder(
    borderRadius: BorderRadius.circular(2.0),
  ),
  side: MaterialStateBorderSide.resolveWith(
      (states) => BorderSide(width: 1.0, color: Colors.red),
  ),
),