设置工具栏颜色和导航栏后退按钮

我想在iOS7中设置工具栏的背景颜色:我用这个设置颜色:

toolBar= [[UIToolbar alloc] initWithFrame:CGRectMake(0,0,320,40)];
[toolBar setBarStyle:UIBarStyleBlack];
toolBar.items = [[NSArray alloc] initWithObjects:barButtonDone,flexible,barButtonOther,nil];
toolBar.tintColor=[UIColor colorWithPatternImage:[UIImage imageNamed:@"dropdownbar"]];

但是背景图像没有显示.

我想知道这是做什么的:

 NSArray *ver = [[UIDevice currentDevice].systemVersion componentsSeparatedByString:@"."];
if ([[ver objectAtIndex:0] intValue] >= 7) {
    self.navigationController.navigationBar.barTintColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"top_bar"]];
    self.navigationController.navigationBar.translucent = NO;
} else {
    self.navigationController.navigationBar.tintColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"top_bar"]];

}

Nd如何更改默认导航栏的后退按钮颜色: