如果验证失败，请将文本框边框颜色设置为红色(扩展控件)

我扩展了文本框控件，为日期格式添加了正则表达式验证器。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel;
using System.Text;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace Myapplication.App_Code
{
    public class DateTextBox  : TextBox
    {
        private RegularExpressionValidator regexval;
        public string InvalidDate="Incorrect date format, must be dd/mm/yyyy";
        public string ClientScript = "true";
        protected override void OnInit(EventArgs e)
        {
            regexval = new RegularExpressionValidator();
            regexval.ControlToValidate = this.ID;
            regexval.ErrorMessage = this.InvalidDate;
            regexval.EnableClientScript = (this.ClientScript.ToLower() != "false");
            regexval.ValidationExpression = "^(0[1-9]|[12][0-9]|3[01])[-/.](0[1-9]|1[012])[-/.](19|20)''d''d$";
            //regexval.Text = "*Incorrect date format";
            regexval.ForeColor = System.Drawing.Color.Red;
            regexval.ValidationGroup = "Tab1";
            Controls.Add(regexval);
            base.OnInit(e);
        }
        protected override void OnPreRender(EventArgs e)
        {
            Attributes.Add("placeholder", "dd/mm/yyyy");
            base.OnPreRender(e);
        }
        protected override void Render(HtmlTextWriter writer)
        {
            base.Render(writer);
            regexval.RenderControl(writer);
        }
    }
}

如果动态添加的正则表达式验证失败，我需要触发一些事件，在其中更改文本框颜色。到目前为止，我只能在使用开箱即用的属性无效时显示"文本"属性或"错误消息"。