navigationBarMutedUnselectedIcon property
If true, the unselected icons in the NavigationBar use a more muted color version of the color defined by navigationBarIconSchemeColor.
If null, the default value depends on the navigationBarIsStyled value. If it is true, this property defaults to true, otherwise to false. If the property is defined, the defined value is used.
A muted unselected icon can only be applied when a defined icon color has been selected. When navigationBarIsStyled this is always the case, but if it is false, you also have to assign a value to navigationBarIconSchemeColor or navigationBarSelectedIconSize or navigationBarUnselectedIconSize, so a none standard IconTheme must be created that can be muted. If none of those properties are defined the widget default behavior for icon style is used, and the unselected icon cannot be muted since all properties are null.
Implementation
final bool? navigationBarMutedUnselectedIcon;