[self.navigationController.navigationBar setBarTintColor:[UIColor purpleColor]];

或者如下，图片高度应该为64像素

[self.navigationController.navigationBar setBackgroundImage:[UIImage p_w_picpathNamed:@"navi_bg"] forBarMetrics:UIBarMetricsDefault];

自定义UINavigationController，很好

https://yq.aliyun.com/articles/31390