I work at an application and I tested today on iOS 7.1. Until now my search bar was normal:
As @dave noted above, you can just use say:
searchBar.backgroundImage = [[UIImage alloc] init];
which avoids the need for the category on UIImage incorporated in @Jugale's example.
My quick fix used some code I found here: https://stackoverflow.com/a/18664917/1153630
And then:
searchBar.backgroundImage = [UIImage imageWithColor:[UIColor clearColor]];
I'm still not very impressed by it though: will update answer when I find a better way.
You may also want to checkout: Colour changed in iOS7.1, how to change searchBar colour?