primaryVariant property
Typically a darker version of the primary color.
In Flutter SDK the primaryVariant color is only used by SnackBar button color in dark theme mode as a part of predefined widget behavior. If you provide a custom SnackBarThemeData where you define SnackBarThemeData.actionTextColor to primary or secondary, this color property becomes a good property to use if you need a custom color for custom widgets accessible via your application's ThemeData, that is not used as default color by any built-in widgets.
Implementation
final Color primaryVariant;