useLegacyColorScheme property
final
This flag is controlling how BottomNavigationBar is going to use
the colors provided by the selectedIconTheme, unselectedIconTheme,
selectedItemColor, unselectedItemColor.
The default value is true as the new theming logic is a breaking change.
To opt-in the new theming logic set the flag to false
Implementation
final bool useLegacyColorScheme;