When I drop a UISearchBar into my view inside Interface Builder, and change its style to Black Opaque, the cancel button stays unfittingly blue / gray and doesn\'t become bl
The problem with your solution is that the code is assuming that the objectAtIndex:3 is the cancel button. Not only does this generate a compiler warning, but also if you are displaying the Cancel button programmatically (for example using [searchBar setShowsCancelButton:YES], you risk crashing the application.
A simpler solution is to set the style of the whole search bar in ViewDidLoad(), using:
searchBar.tintColor = [UIColor colorWithWhite:0.3 alpha:1.0];
this overrides the style set in the Interface Builder BUT also changes the colour of the Cancel button to be same colour as the whole bar (although it doesn't let you set the style of Cancel button independently, unfortunately.