I was inspired by your answers and here is how I fixed it. First, in the method that calls for the messages app to be displayed, I set the image of the nav bar to nil which takes it back to the default appearance.
[[UINavigationBar appearance] setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];
Then in my viewWillAppear method for the view controller that the user goes back to, I simply used this code again
[[UINavigationBar appearance] setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];