1. textField.placeholder = @"username is in here!";
2. [textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];
3. [textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];

这里是使用了KVC的方式

参考链接

http://www.cnblogs.com/isItOk/p/5791644.html

http://www.cnblogs.com/isItOk/p/5651904.html

http://www.cnblogs.com/isItOk/p/5791638.html

http://www.cnblogs.com/isItOk/p/5651898.html

http://www.cnblogs.com/isItOk/p/6582859.html