在MFMailComposeViewController中更改导航的主标题颜色

I haven't problem for change color of main title of navigation on a normal viewController but on a MFMailComposeViewController, it isn't possible. I can change colors of buttons (cancel and send), I can set background of navigation bar but not possible to change color of title. I don't want set a new title (apparently, it's not allow by Apple), I just want change the color :'(I haven't problem for change color of main titl