The top level list item is named .submenu, so all links in that, including the top link, are affected. Change the rules to
Code:
#nav-cat li.submenu ul a {
   color: #fff;
}

#nav-cat li.submenu ul a:hover {
   color: #87ceeb;
}
This will apply only to subcategory links.

Also change the order of the rules so the hover state if active will override the base state.