Theme TwentyEleven Drop Down menu colour

Hi, I would like to know how to change the colour of the drop down menu background. My site is http://www.thegoodshelfcompany.com if you click on one of the product headings you will see that the background changes to mirror the background of the page and the text is no longer readable. I would like to know how to change this but can it find it in the editor. I am quite new at this and find the themes very limiting but have a hard time deciphering the code. Any help would be much appreciated.