anchor.diff:    /// [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].
  +  ///
  +  /// To ensure that an app is accessibile, a contrast ratio of 4.5:1 for [primary]
  +  /// and [onPrimary] is recommended. See
  +  /// <https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html>.
     final Color onPrimary;
   
     /// A color that's clearly legible when drawn on [secondary].
  +  ///
  +  /// To ensure that an app is accessibile, a contrast ratio of 4.5:1 for [secondary]
  +  /// and [onSecondary] is recommended. See
  +  /// <https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html>.
     final Color onSecondary;
   
     /// A color that's clearly legible when drawn on [surface].
  +  ///
  +  /// To ensure that an app is accessibile, a contrast ratio of 4.5:1 for [surface]
  +  /// and [onSurface] is recommended. See
  +  /// <https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html>.
     final Color onSurface;
   
  +  /// A color that's clearly legible when drawn on [background].
  +  ///
  +  /// To ensure that an app is accessibile, a contrast ratio of 4.5:1 for [background]
  +  /// and [onBackground] is recommended. See
  +  /// <https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html>.
  +  final Color onBackground;
  +
     /// A color that's clearly legible when drawn on [error].
  +  ///
  +  /// To ensure that an app is accessibile, a contrast ratio of 4.5:1 for [error]
  +  /// and [onError] is recommended. See
  +  /// <https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html>.
     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;
  
positive.code: 
    /// 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,
  
negative.code:   /// A darker version of the secondary color.
    final Color secondaryVariant;
  
    /// The background color for widgets like [Card].
    final Color surface;
  
    /// A color that typically appears behind scrollable content.
    final Color background;
  
  