A repeater is one of the web-databound controls that, well, it repeats items. So there are normally more than one item. That's why you cannot access it directly. It sits in a different NamingContainer
which is the RepeaterItem
of the repeater.
However, the control that raised an event is always the sender
argument. So you just need to cast it:
protected void Buttonlink_Click(object sender, System.EventArgs e)
{
LinkButton linkbtTitle = (LinkButton ) sender;
linkbtTitle.ForeColor = System.Drawing.Color.HotPink;
}