Changing navigation bar back button text (

Hi,

I need to customize the text and color of navigation bar back button text and '<' to white.

For back button text , am doing like this

In appdelegate,

UIBarButtonItem.Appearance.SetTitleTextAttributes(new UITextAttributes ()
{
TextColor=UIColor.White

            },UIControlState.Normal); 

and for changing text in my page,

NavigationPage.SetBackButtonTitle (this, "Back");

but it displays like as shown in the attachment. by default it is taking the blue color.
How can i change that blue color?

Please suggest me on this.

Thanks in advance...