anchor.diff:  
     static Brightness _brightnessFor(Color color) => ThemeData.estimateBrightnessForColor(color);
   
  +  /// The color displayed most frequently across your app’s screens and components.
     final Color primary;
  +
  +  /// A darker version of the primary color.
     final Color primaryVariant;
  +
  +  /// An accent color that, when used sparingly, calls attention to parts
  +  /// of your app.
     final Color secondary;
  +
  +  /// A darker version of the secondary color.
     final Color secondaryVariant;
  +
  +  /// A color that typically appears behind scrollable content.
     final Color background;
  +
  +  /// The color to use for input validation errors, e.g. for
  +  /// [InputDecoration.errorText].
     final Color error;
  +
  +  /// The background color for widgets like [Card].
     final Color surface;
  +
  +  /// A color that's clearly legible when drawn on [primary].
     final Color onPrimary;
  +
  +  /// A color that's clearly legible when drawn on [secondary].
     final Color onSecondary;
  +
  +  /// A color that's clearly legible when drawn on [surface].
     final Color onSurface;
  +
  +  /// A color that's clearly legible when drawn on [error].
     final Color onError;
  +
  +  /// A color that's clearly legible when drawn on [background].
     final Color onBackground;
  +
  +  /// The overall brightness of this color scheme.
     final Brightness brightness;
   
  +  /// Creates a copy of this color scheme with the given fields
  +  /// replaced by the non-null parameter values.
     ColorScheme copyWith({
       Color primary,
       Color primaryVariant,
  
positive.code:        assert(onError != null),
         assert(brightness != null);
  
    const ColorScheme.dark({
      this.primary = const Color(0xffbb86fc),
      this.primaryVariant = const Color(0xff4b01d0),
  
negative.code:        assert(onError != null),
         assert(brightness != null);
  
    /// Create a color scheme from a [MaterialColor] swatch.
    ///
    /// This constructor is used by [ThemeData] to create its default \
    /// color scheme.
    factory ColorScheme.fromSwatch({
      MaterialColor primarySwatch = Colors.blue,
      Color primaryColorDark,
  