ios – 如何更改UINavigationController背景颜色？

@implementation UINavigationBar (UINavigationBarCategory)

- (void)drawRect:(CGRect)rect {

    UIImage *img  = [UIImage imageNamed: @"navController.png"];
    [img drawInRect:CGRectMake(0,self.frame.size.width,self.frame.size.height)];
        self.tintColor = [UIColor blueColor];
}

@end

背景是我想要的和tintColor,但是当试图设置UIColor类中不存在的颜色时,它会失败并显示奇怪的颜色：

@implementation UINavigationBar (UINavigationBarCategory)

- (void)drawRect:(CGRect)rect {

    UIImage *img  = [UIImage imageNamed: @"navController.png"];
    [img drawInRect:CGRectMake(0,self.frame.size.height)];
        self.tintColor = [UIColor colorWithRed:(26/255) green:(103/255) blue:(159/255)                      alpha:1];
}

@end

如何强制UINavigationBar显示我想要的颜色？

注意：我只对导航控制器按钮颜色有问题,因为背景本身设置为图像.