Set TabbedPage icons at runtime?

I'm trying to implement an interface to let my user know when certain data has been flagged. The cleanest way to do this is by changing the icons in my TabbedPage - which I'm having some trouble doing.

I hoped that maybe switching the "Icon" property on my Forms Page would change it in the tab bar but no dice. Here's my snippet - if anyone could look it over and maybe help figure out what else I need to do that'd be great

//This is in the TabbedPage
//Pages is a Dictionary<string, NavigationPage>
//Children maps to pages
public void FlagNotifications(bool hasNotifications)
{

    if (hasNotifications)
    {
        Device.BeginInvokeOnMainThread(() =>
        {
           pages["Notifications"].Icon = (FileImageSource)ImageSource.FromFile("icon_notifications_accent.png");
        });
    }
    else {
        Device.BeginInvokeOnMainThread(() => 
        {
           pages["Notifications"].Icon = (FileImageSource)ImageSource.FromFile("icon_notifications.png");
        });
    }

}