Menu Appears Black in Internet Explorer

I have a navigation menu with a background color and then with a grey color that appears when the mouse is over the menu. This works fine in Mozilla and Chrome.

However, in Internet Explorer, the menu appears as black.

Can anyone advise on how to fix this?

Here is what I think is the relevant code in my style sheet:

.secondary-navigation ul ul {
background: white;
border: 1px solid #dddddd;
-webkit-box-shadow: 0 0 5px 0 rgba(0, 0, 0, 0.1);
-moz-box-shadow: 0 0 5px 0 rgba(0, 0, 0, 0.1);
box-shadow: 0 0 5px 0 rgba(0, 0, 0, 0.1);
display: none;
left: 0;
position: absolute;
top: 100%;
width: 150px;
z-index: 99;