Jen - You would need to target the individual links with CSS. You could use variations of the :hover state from the CSS file. Specifically, this line.
#navcontainer ul li a:hover {background-color : #494949;color : #eee;}
I would change the background-color property to be the yellow that you want and then the others could be targeted with the other colors for the hover states.
The navigation that is generated by the template (from my demo site).:
<div id="navcontainer">
<ul class="navlist">
<li class="page_item"><a href="http://iamww.com/wpthemes">home</a></li>
<li class="page_item page-item-76 current_page_item">
<a href="http://iamww.com/wpthemes/about-2/" title="About">About</a></li>
<li class="page_item page-item-80"><a href="http://iamww.com/wpthemes/example-images/"
title="Example Images">Example Images</a></li>
<li class="page_item page-item-88"><a href="http://iamww.com/wpthemes/archives/"
title="Archives">Archives</a></li>
<li class="page_item page-item-79"><a href="http://iamww.com/wpthemes/element-examples/"
title="Element Examples">Element Examples</a></li>
<li class="headright"><a href="javascript:;" onmousedown="toggleDiv('slickbox');"
title="Browse the archives">browse ↓</a></li>
</ul>
</div>
Say your "about" page is then page-item-76. The number at the end is the ID of the page... You could then change that hover state to black (or whatever color you want to) by adding this line of CSS below the one mentioned above.
#navcontainer ul li.page-item-76 a:hover {background-color : #000;}
This would overwrite the previous value of yellow and set the background-color of the hover state to black on only that li element. You would then just continue targeting your other links...
Hope that helps.