[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];
[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];
ios修改textField的placeholder的字体颜色、大小
原文：http://www.cnblogs.com/deneyZhao/p/5038614.html