I don't know how your menu works so I don't know if this is possible, but if the subnavs were inside the list of primary menus, then the code would be quite simple:
Code:
ul#stlprimary li:hover {
background-color:#900;
color: #fff;
}
Menu would roughly look like this:
HTML Code:
<ul id="stlprimary">
<li><a href="#">Main</a>
<ul id="stlsubnav">
<li><a href="#">Sub</a></li>
</ul>
</li>
</ul>
Then hovering over the subnavs would be like hovering over the primary, since the subnavs would be inside the primary. Then you could assign the subnavs their own hover colors.
If it's not possible with your code to put the subnavs inside the primary list items, then I think you'll have to use javasript for this.
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