What is difference between primary and onPrimary properties in ColorScheme Flutter-CodePudding

While defining ThemeData of the Flutter app, we can define colorScheme property. This property has inner-properties such as background & onBackground, primary & onPrimary, secondary & onSecondary, etc. Also, all these properties are set as required.

  static final ThemeData lightTheme = ThemeData(
    colorScheme: ColorScheme(
      background: appBackgroundColor,
      brightness: Brightness.light,
      error: Colors.white,
      onBackground: primaryColor,
      one rror: null,
      onPrimary: null,
      onSecondary: null,
      onSurface: null,
      primary: null,
      secondary: secondaryColor,
      surface: null,
    ),
  );

I tried referring the

check this : The color system

CodePudding user response：

Many of the colors have matching 'on' colors, which are used for drawing content on top of the matching color. For example, if something is using primary for a background color, onPrimary would be used to paint text and icons on top of it. For this reason, the 'on' colors should have a contrast ratio with their matching colors of at least 4.5:1 in order to be readable.

Got this from https://api.flutter.dev/flutter/material/ColorScheme-class.html