修改UISearchBar背景色

//iOS7.1
[[[[_searchBar.subviews objectAtIndex:0] subviews] objectAtIndex:0] removeFromSuperview];
[_searchBar setBackgroundColor:[UIColor colorWithRed:245.f/255.f green:238.f/255.f blue:219.f/255.f alpha:1]];

//iOS7.0
[_searchBar setBarTintColor:[UIColor clearColor]];
[_searchBar setBackgroundColor:[UIColor colorWithRed:245.f/255.f green:238.f/255.f blue:219.f/255.f alpha:1]];

//iOS7.0以下
[[_searchBar.subviews objectAtIndex:0] removeFromSuperview];
[_searchBar setBackgroundColor:[UIColor colorWithRed:245.f/255.f green:238.f/255.f blue:219.f/255.f alpha:1]];