Drop-down menu background colour in tdSimple

I’m using the tdSimple theme here:

http://webindexing.biz/terraintest/photographers/paul-mallam/

It’s ideal except for the fact that the background colour behind the items in the drop-down menu is white instead of grey. I’ve tinkered with the CSS to no avail, and I’ve written to the theme designer but haven’t got a reply. Below is the submenu element from the page as it appears in Chrome. Can anyone suggest a way to change the background colour?

Thanks,

Jon.

<ul class=”sub-menu”>
<li id=”menu-item-75″ class=”menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-67 current_page_item menu-item-75″>Paul Mallam
<li id=”menu-item-74″ class=”menu-item menu-item-type-post_type menu-item-object-page menu-item-74″>Peter McMahon
<li id=”menu-item-73″ class=”menu-item menu-item-type-post_type menu-item-object-page menu-item-73″>Peter Lang