Display online users as green and offline as grey using real time updates in ASP.Net

First you need to have the column as Active (means logged In) as Bit. You need to show All the Users in Repeater Control. Consider this example.

HTML

<asp:Repeater ID="Repeater1" runat="server" OnItemDataBound="Repeater1_OnItemDataBound">
    <HeaderTemplate>
        <table border="0" cellpadding="0" cellspacing="0">
            <tr>
                <th align="left">
                    Name
                </th>
            </tr>
    </HeaderTemplate>
    <ItemTemplate>
        <tr>
            <td>
                <asp:Label ID="lblName" Text='<%# Eval("Name") %>' runat="server"></asp:Label>
                <asp:HiddenField ID="hfStatus" Value='<%# Eval("Status") %>' runat="server" />
            </td>
        </tr>
    </ItemTemplate>
    <FooterTemplate>
        </table>
    </FooterTemplate>
</asp:Repeater>

Namespaces

using System.Data;
using System.Drawing;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[2] { new DataColumn("Name", typeof(string)),
                    new DataColumn("Status", typeof(bool))});
        dt.Rows.Add("John Hammond", true);
        dt.Rows.Add("Mudassar Khan", false);
        dt.Rows.Add("Suzanne Mathews", true);
        dt.Rows.Add("Robert Schidner", false);
        Repeater1.DataSource = dt;
        Repeater1.DataBind();
    }
}
protected void Repeater1_OnItemDataBound(object sender, RepeaterItemEventArgs e)
{
    if (e.Item.ItemType == ListItemType.AlternatingItem || e.Item.ItemType == ListItemType.Item)
    {
        if (Convert.ToBoolean((e.Item.FindControl("hfStatus") as HiddenField).Value) == true)
        {
            (e.Item.FindControl("lblName") as Label).ForeColor = Color.Green;
        }
        else
        {
            (e.Item.FindControl("lblName") as Label).ForeColor = Color.Gray;
        }
    }
}

Screenshot