UITextField設置placeholder顏色

方式一：

_codeTextField.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"請輸入驗證碼(4位數字)" attributes:@{NSForegroundColorAttributeName:[UIColor colorWithHex:kTextLightGray]}];

方式二：KVC方式

_phoneTextField.placeholder = @"請輸入手機號碼";

 [_phoneTextField setValue:[UIColor colorWithHex:kTextLightGray] forKeyPath:@"_placeholderLabel.textColor"];