Ya, you can create a 1px by 1px "blue colored" image and use the following:
[yourButton setBackgroundImage:[UIImage imageNamed:@"theImageYouMade.png"] forState:UIControlStateHighlighted];
You can't use "setImage:" in my method because the highlighted state of the button will actually just display the 1px by 1px image in the center of the button.
My method works for variable sized buttons. Using setImage: requires you to make images that are exactly the same size as your button.
-Chris