I found the answer to this on SO a while back, but I don't recall where. Here's the code that I'm using to set the color of the text.
[[UIBarButtonItem appearanceWhenContainedIn:[UISearchBar class], nil] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
[UIColor redColor],NSForegroundColorAttributeName,
//[UIColor whiteColor],UITextAttributeTextShadowColor,
//[NSValue valueWithUIOffset:UIOffsetMake(0, 1)],UITextAttributeTextShadowOffset,
nil]
forState:UIControlStateNormal];