Hi
if u want to change the background color of link when u clicked, u can use some server side logic if jquery or css is not working for you
try this in your about us's or any page's pageload event
HtmlAnchor link = (HtmlAnchor)(this.Master).FindControl("controlid");
link.Style.Add("background-color", "#ffffff");
Background color of link will persist until u move to another page.
Note:This code is for html anchor tag.Replace with ur html tag or asp control