backgroundColor property Null safety
The fill color to use for an app bar's Material.
If null, then the AppBarTheme.backgroundColor is used. If that value is also null, then AppBar uses the overall theme's ColorScheme.primary if the overall theme's brightness is Brightness.light, and ColorScheme.surface if the overall theme's brightness is Brightness.dark.
This property is used to configure an AppBar.
final Color? backgroundColor;