设置textField的placeholder字体的颜色，默认是灰色

//设置textField的placeholder字体的颜色，默认是灰色
 UIColor *color = [UIColor whiteColor];

 self.loginNumText.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"请输入用户名" attributes:@{NSForegroundColorAttributeName: color}];