也许你想尝试这种方式，但苹果可能会警告你访问私有ivar:

[self.myTextField setValue:[UIColor darkGrayColor] 
                forKeyPath:@"_placeholderLabel.textColor"];

请注意 根据Martin Alléus的说法，iOS 7不再适用了。

自从ios6在UIViews中引入了带属性字符串，就可以像这样为占位符文本分配颜色:

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.
}

[txt_field setValue:ColorFromHEX(@"#525252") forKeyPath:@"_placeholderLabel.textColor"];

以下仅适用于iOS6+系统(如Alexander W的评论所示):

UIColor *color = [UIColor grayColor];
nameText.attributedPlaceholder =
   [[NSAttributedString alloc]
       initWithString:@"Full Name"
       attributes:@{NSForegroundColorAttributeName:color}];

你可以重写drawPlaceholderInRect:(CGRect)rect来手动渲染占位符文本:

- (void) drawPlaceholderInRect:(CGRect)rect {
    [[UIColor blueColor] setFill];
    [[self placeholder] drawInRect:rect withFont:[UIFont systemFontOfSize:16]];
}

有了这个，我们可以在iOS中改变文本字段占位符文本的颜色

[self.userNameTxt setValue:[UIColor colorWithRed:41.0/255.0 green:91.0/255.0 blue:106.0/255.0 alpha:1.0] forKeyPath:@"_placeholderLabel.textColor"];