Материал из .Net Framework эксперт
Change invalid control"s background color (C#)
<%@ Page Language="C#" %>
<script runat="server">
void Page_PreRender()
{
foreach (BaseValidator valControl in Page.Validators)
{
WebControl assControl = (WebControl)Page.FindControl(valControl.ControlToValidate);
if (!valControl.IsValid)
assControl.BackColor = System.Drawing.Color.Yellow;
else
assControl.BackColor = System.Drawing.Color.White;
}
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title>Show Validators</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Label
id="lblFirstName"
Text="First Name"
AssociatedControlID="txtFirstName"
Runat="server" />
<br />
<asp:TextBox
id="txtFirstName"
Runat="server" />
<asp:RequiredFieldValidator
id="reqFirstName"
ControlToValidate="txtFirstName"
Text="(Required)"
EnableClientScript="false"
Runat="server" />
<br /><br />
<asp:Label
id="lblLastName"
Text="Last Name"
AssociatedControlID="txtLastName"
Runat="server" />
<br />
<asp:TextBox
id="txtLastname"
Runat="server" />
<asp:RequiredFieldValidator
id="reqLastName"
ControlToValidate="txtLastName"
Text="(Required)"
EnableClientScript="false"
Runat="server" />
<br /><br />
<asp:Button
id="btnSubmit"
Text="Submit"
Runat="server" />
</div>
</form>
</body>
</html>