i have some custom bar button items in my navigation controller.

(maxi
In iOS 7, a navigation bar’s tintColor affects the color of the back indicator image, button titles, and button images. The barTintColor property affects the color of the bar itself. So, you can try setting the barTintColor and check if it solves your issue.
Also, when using the barButtonItem images, the following code is worth a try:
myImage = [myImage imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];