Objective-C更改placeholder字体颜色

法一：
self.nameTextField.placeholder =
@"Username (NOT Email Address)";
[self.nameTextField
setValue:[UIColor
whiteColor] forKeyPath:@"_placeholderLabel.textColor"];
法二：
NSAttributedString * placeholder= [[NSAttributedString
alloc] initWithString:@" Username(NOT Email Address)"
attributes:@{NSForegroundColorAttributeName: [UIColor
whiteColor]}];
self.nameTextField.attributedPlaceholder = placeholder;