改变UITextField的Placeholder颜色

if([textField respondsToSelector:@selector(setAttributedPlaceholder:)]
{
UIColor*color =[UIColor blackColor];
textField.attributedPlaceholder =[[NSAttributedString alloc] initWithString:placeholderText attributes:@{NSForegroundColorAttributeName: color}];
}else{
NSLog(@"Cannot set placeholder text's color, because deployment target is earlier than iOS 6.0");
// TODO: Add fall-back code to set placeholder color.
}