I have a UINavigationItem, but I can\'t found anything beside tittle, prompt, and back button in attribute inspector
You shouldn't use the background property of UINavigationBar, but instead you should use barTintColor like this:
self.navigationController.navigationBar.barTintColor = UIColor.redColor()
As written in the official documentation to change the bar background you have to access to the barTintColor property:
The tint color to apply to the navigation bar background.
If you want to edit the style of the navigation bar such as button color you should access to the barTint property. If you want to edit the style of an navigationItem such as back button you should edit the button property, not the UINavigationItem's.