It’s a hack but it works: https://gist.github.com/anonymous/e34c6f9403c120501dd42f14164567e0
Use like this <AndroidStatusBarHack IsLight="true" />
Note that IsLight="true" corresponds to View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR in Android. In other words you say that the status bar itself is light and thus you want the darker text.
You can of course freely use the code to define a better API. 