sorry, copied the wrong code try this
HTML Code:
/* ================================================ */
/* how to highlight parent of current page */
/* ================================================ */
ul.rMenu li.current_page_parent a:link,
ul.rMenu li.current_page_parent a:active,
ul.rMenu li.current_page_parent a:hover,
ul.rMenu li.current_page_parent a:visited,
ul.rMenu li.current_page_parent {
background: #00ffff !important;
}
/* ++++++++++++++++++++++++++++++++++++++++++++++++++ */
Note if you have A the parent of B the parent of C and you are on page C, this will only highlight B, if you want A and B highlighted use current_page_ancestor instead of current_page_parent