http://stackoverflow.com/questions/14523348/how-to-change-the-background-color-of-a-uibutton-while-its-highlighted

UIButton只能设置按下的背景图片，所以我们可以曲线救国，将背景色转换为一张图片

Return an image made from the highlight colour you want. This could also be a category.

+ (UIImage *)imageWithColor:(UIColor *)color {
   CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
   UIGraphicsBeginImageContext(rect.size);
   CGContextRef context = UIGraphicsGetCurrentContext();

   CGContextSetFillColorWithColor(context, [color CGColor]);
   CGContextFillRect(context, rect);

   UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

   return image;
}

and then change the highlighted state of the button:

[myButton setBackgroundImage:[self imageWithColor:[UIColor greenColor]] forState:UIControlStateHighlighted];