А для iOS 7+ вы делаете следующее:
Objective-C
UIImage *image = [[UIImage imageNamed:@"myImage.png"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIBarButtonItem *button = [[UIBarButtonItem alloc] initWithImage:image style:UIBarButtonItemStylePlain target:self action:@selector(YOUR_METHOD:)];
Swift 2,3
let image = UIImage(named: "myImage")?.imageWithRenderingMode(.AlwaysOriginal)
let button = UIBarButtonItem(image: image, style: .Plain, target: self, action: #selector(YOUR_METHOD(_:)))
Swift 3.0
let image = UIImage(named: "myImage")?.withRenderingMode(.alwaysOriginal)
let button = UIBarButtonItem(image: image, style: .plain, target: self, action: #selector(YOUR_METHOD(_:)))