changeAccentColor method
Implementation
void changeAccentColor(Color? color) {
final newDarkTheme = darkTheme.copyWith(colorScheme: ColorScheme.fromSwatch().copyWith(secondary: color));
final newLightTheme = lightTheme.copyWith(colorScheme: ColorScheme.fromSwatch().copyWith(secondary: color));
darkTheme = newDarkTheme;
lightTheme = newLightTheme;
notifyListeners();
}