backgroundColor property
final
The button's background color.
If this property is null, then the FloatingActionButtonThemeData.backgroundColor of ThemeData.floatingActionButtonTheme is used. If that property is also null, then the ColorScheme.primaryContainer color of ThemeData.colorScheme is used. If ThemeData.useMaterial3 is set to false, then the ColorScheme.secondary color of ThemeData.colorScheme is used.
Implementation
final Color? backgroundColor;