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To change the back button chevron color for a specific navigation controller*:

self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

*If you are using an app with more than 1 navigation controller, and you want this chevron color to apply to each, you may want to use the appearance proxy to set the back button chevron for every navigation controller, as follows:

[[UINavigationBar appearance] setTintColor:[UIColor whiteColor]]; 

To change the back button chevron color for a specific navigation controller*:

self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

*If you are using an app with more than 1 navigation controller, and you want this chevron color to apply to each, you may want to use the appearance proxy to set the back button chevron for every navigation controller, as follows:

[[UINavigationBar appearance] setTintColor:[UIColor whiteColor]]; 

And for good measure, in swift (thanks to Jay Mayu in the comments):

UINavigationBar.appearance().tintColor = UIColor.whiteColor() 

To change back button chevron color throughout the entire app* do this:

self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

*Note that if you are using more than 1 UINavigationController, you will have to set this for each one.

To change the back button chevron color for a specific navigation controller*:

self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

*If you are using an app with more than 1 navigation controller, and you want this chevron color to apply to each, you may want to use the appearance proxy to set the back button chevron for every navigation controller, as follows:

[[UINavigationBar appearance] setTintColor:[UIColor whiteColor]]; 

To change back button chevron color throughout the entire app* do this:

self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

*Note that if you are using more than 1 UINavigationController, you will have to set this for each one.

The accepted answer could have undesirable side-effects, as you will be theming the entire app instead of just the back button, which is what the original question asks how to do.

To change back button chevron color throughout the entire app* do this:

self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

*Note that if you are using more than 1 UINavigationController, you will have to set this for each one.